I think Ken Horner has built 1000cc versions of the Irving Vincent. The one he took to Goodwood Revival two years ago was not a biggie. It was still bloody fast.
A few years ago, we had Sounds Of Singles in Australia. All the bike had to have was a four stroke single cylinder engine. There were no other rules. The lack of capacity limit killed the class. Only the guys with the big motors could really be competitive and the big motors blew up very often. Nobody could afford to race regularly in that class and have any hope of winning. 500cc is about as big as you can have a single and still have reliability. For twins, a capacity limit of 1000cc and air-cooled would make a very good race class. In any case a bigger motor is not always necessarily better. One of the things which holds big twins back, is heat build-up.
1000cc Irving Vincent ? :