3/75 isn't the same as HQ. Once HJ got a canister late in 1974 the carby number changed, and it is the same carby for auto and manual. Manual has the vacuum advance connected to a ported vacuum port off a T-piece with the canister from memory, auto vac advance connects to the back of the carb (port has a rubber plug on the manual). I think the carby body number is 7045281. Earlier HJ manual without canister is 7043281 from memory again. I'll check when i'm home.