I'm sure the Formula 1 and Formula 2 specs were based around the engine being road based/derived. I think it was done so that on paper the costs would be kept down. Internals could be changed but there were rules n regs about the stock road bike external crankcases/barrels/heads etc having to look the same outward appearance - certainly an F2 350 Yamaha had to run stock cases, barrels heads etc but you could fit a dry TZ clutch, TZ pipes, TZ radiator etc all in a racing rolling chassis. I'm going a long way back to when I was spannering here early 80's so I could have forgot/mixed up/imagined some of this - if i have please let me know