you are trying to open a can of worms here.the problem you will face is the preproduction theory.my older brother tried this with tt500 yamahas as there were a few in the USA pre 1975,ma would not approve as they were preproduction.i can prove preproduction racing of 4 valve weslakes in 1974.the 2 valve dirt track and longtrack eligibility would have to be re written.try as this would open up other bikes for pre date racing