“Bob drew the new upright,” remembers Head. “Quite simple, but it was drawn in half a day. Thirty-six hours later, two aluminium castings to the new design were delivered. Six hours later, they came out of the machine shop. Two hours later, they were on the car. New bodywork was delivered from Specialised Mouldings and the car was transported to the USA, less than three days after the change had been initiated.”

Three days. A completely redesigned race car from the cockpit forward. Even at the end of a long career in motor racing that saw him become one of the most successful designers in F1 history as co-founder of and technical director of the Williams Formula 1 team, it remained one of the most remarkable things with which Head had been involved.

At Mosport, Stewart planted the freshly reconstituted T260 on pole by seven-tenths of a second over Denny and Peter. Oh, not that Peter. The other one, Revson. Over the winter, McLaren had decided to replace the jockey-sized Gethin in Can-Am with matinee-idol Revvie. Twenty-six cars in all would start the race, but for all intents and purposes, these were the only three cars that mattered. Next was Canadian John Cordts in an older McLaren M8C, more than two seconds behind.

Baulked by a sticking throttle, the Mod Scot polesitter watched Hulme lead the early laps. By lap 10, he’d come to terms with the issue and put the cigarette box in front. Nine laps later, the Lola rolled to a stop, its differential seized.

It would be the story of the season.

At Mont-Tremblant Denny put the McLaren on pole, but Jackie was right beside him. Again, Hulme shot into the lead. Again, Stewart found a way by, this time aided by the fact that Hulme was battling a stomach virus. By the end of the race Stewart had scored his first victory in the T260 and McLaren had been vanquished for only the second time since 1968.

On to Road Atlanta the circus went, and here Stewart was at his most masterful. This time the Lola was a full second from pole, but when the flag fell, Stewart seemed to find reserves of speed only he could. He passed Hulme on lap three, Revson on lap eight, but a deflating tyre forced him to pit on lap 13, dropping three laps down. The race was over, but not the spectacle. The normally silky-smooth Stewart began flinging the T260 around the track at impossible angles, scrabbling for every last speck of grip.

Barry Smyth, doing PR for the rival McLaren team, still sounds awestruck: “He looked like a sprint car driver, he had it hung out so far. He just drove the wheels off that car.”

“Stewart got the absolute maximum out of that car,” says Marston. “I think at that time he was absolutely at his driving peak.”

Stewart ultimately set the fastest lap, 0.3sec faster than Hulme’s pole time. It also equalled precisely the time the Chaparral sucker car had set the previous year. In the end, it was the Lola that gave up, not the Scot. The T260 limped into the pits on lap 62, its right rear shock having tapped out.

By the next race it was clear the orange cars’ fifth straight title was safe. There were two of them against one Lola, and Stewart fell too far behind in the points race due to mechanical issues to make up the deficit. At the Glen, Stewart once again put the T260 on pole. Once again, the car let him down.

Stewart had managed to lead all four races to date in a clearly inferior car but only finished one of them. “The car was extremely difficult to drive,” he recalls. “It had a very short wheelbase and the aerodynamics… I don’t think there was a wind tunnel being used, it was just a wet finger in the air, I think.”

“The car was very short of downforce relative to the McLarens,” remembers Head. “Particularly at the front. The holes in the upper front surface were an attempt to reduce lift at the front, [but] I doubt that they were effective. The car had ostensibly been tested in Specialised’s wind tunnel, but the measuring of balance forces was terrible, and I doubt that anything was learned.

“Jackie managed to win a couple of races, but this would be due to him, not the car.”

At Mid-Ohio, Stewart would once again wrestle the T260 into the lead – and keep it there. But it was his wrangling over safety that made the headlines and very possibly saved Hulme’s life. As normal, Jackie began with a walk of the course. Mid-Ohio is one of the most picturesque tracks in North America, but Stewart was appalled.

“It was ludicrous. There was a left-hand bend after the start/finish line, and if you’d gone off on that high-speed corner in an 850-horsepower Can-Am car, there was one tree that was very obvious that you were going to go straight into,” he says.

The Scot marched into track owner Les Griebling’s office.

“I said, ‘Look, this is ridiculous. You’ve got to cut the tree down.’ And they just didn’t want to do it. So I announced that I was going to withdraw from the race if they didn’t because, y’know, you can knock a tree down and you can replant other trees, but in a safe place.”

Griebling didn’t blink. Neither did Stewart. The night before the race, the tree was still there. The next morning, it was gone. Tree. Stump. Everything. Just a flat brown patch of dirt remained.

Many disagreed with Stewart, including series commissioner Stirling Moss, who leaned into the conversation at one point and said, “Oh, Jackie. If you’re so concerned about the damn tree, just don’t hit it.”

But the critics were silenced within moments of the green flag.

“On the very first flying lap,” says Stewart, “Denny Hulme went off on that very corner” – a driveshaft had broken under full acceleration on the bumpy course – “and the trajectory of the car went exactly over the cut-down tree.”

By the final two Can-Am races, at Laguna Seca and Riverside, McLaren had again clinched the championship, this time with Peter Revson grabbing the laurels after five victories to Denny’s three and Jackie’s two, including a sensational last-to-first sprint at Road America. (A schedule conflict with an Indycar race led Revson to miss qualifying and start from the back.) It was Revson’s first major championship.

At Laguna Seca, Stewart, Marston and Broadley continued to hunt for aerodynamic answers to the T260’s problem-child ways. And once again, there were safety issues to attend to – this time at the Corkscrew, one of the most famous sequences of turns in all of motor sport.

“There’s trees in front of the barriers, for God’s sake,” says Stewart. “So I said, ‘Listen, we can’t have this’.”

As with Mid-Ohio, the trees came down. But not before Stewart was met with a withering attack from San Francisco Chronicle columnist Gordon Martin, who headlined his story, “Can auto racing afford Jackie Stewart?”

The real question was: could auto racing afford not to follow Stewart?

“I made a decision that I wouldn’t drive in Can-Am unless I was in a McLaren”

Another season had come to a close. An American had won the Canadian-American Challenge for the first time, McLaren had won the championship for the fifth straight year and there were signs for and against the Orange Elephants continuing their reign for a sixth. Before the end of the season, Jackie Stewart announced that he had had enough of driving his heart out in an outclassed car.

“I made a decision that I would not drive again in Can-Am next year unless I was going to drive for McLaren,” says the Scot. “And we signed a contract.”

Lola, too, would return but with a radical new car for new boy David Hobbs. Howden Ganley was looking forward to a full season with the promising BRM.

And now the 917s had been ruled out of the World Sportscar Championship, Porsche was going to turn its attention to Can-Am, led by Roger Penske and Mark Donohue and powered, it was rumoured, by a turbo flat-12 or a naturally aspirated 7-litre 16-cylinder engine.

It had every promise of being the most exciting season in Can-Am history.