He was never given much credit by Brabham for the brilliant design work he did on that engine. To put it in perspective, consider Henry Ford Jr.'s 1960s quest to win the world's most coveted Auto race trophy- the 24 hr Lemans.
It is to auto racing what the IOM TT is to us, the ultimate prize.
Ford first tried to make an outright purchase of Ferrari for a steal of a deal at the time, something like 15 million. Ferrari agreed, then changed his mind and reneged on the deal. So Ford spent many times this amount to wrestle the trophy from Ferrari, Porsche and the other established Leman winners. Some years Ford would enter 5 cars and none would finish, on fire, broken and failed. Eventually, after teaming with Carrol Shelby and spending many more millions on development, they got the job done in rather spectacular fashion.
Compare this to Irving's acheivment at Lemans. Vincent is long since bankrupt, Irving is back home designing tractor engines or what have you when Brabham asks Irving if he could design an V8 engine for an assault on the 24 hr race. Irving does so in his usual all out, hands on manner and the bloody thing wins the 24 hr Lemans first time out! Btw, the Repco V8 has the exact same inspection caps as my Vincent uses, minus the Vincent logo.
Very few people even know the story, hopefully a few more do now.
Glen