As far as I know and found out, is that the CB750 racing type was the four bikes that Honda built for Daytona 200 in 1970. some people say that they have a different steel in the frame. It also have a welded bracket on the frame for the steering damper. As for the engine, it looks right that it has 61.5mm bore, as it was max. 750ccm that counts.
In 71 or 72, Honda built some CR750, where CR stands for Client Racer, and then introduced the racing kit that was sold for private racers. The CR has hinged clip-ons, and a separate bracket for the steering damper, placed where the ignition bracket is. The first series of CR-parts was numbered 970 and there was a later series and modifications that got 971. As the first series of CR31 carbs was sandcasted, the later was diecasted and got number 971. Most of the engine parts is different from a stock engine.
Do you have some photo's to share? I am soon start to build a Cr750 myself, and have collected some parts for it, but it is a long way to go...
Jan
