I seem to remember that Duncan Macdonald offered a service to mod Bultaco frames to Dave Thorpes works spec back in the 70's.
Would these be allowed? To my mind they should be, as should a ty250 twinshock with shocks moved to replicate a majesty.
I think we all know its going down the pre65 route so why not just let it happen without getting stressed but just have fun.
Organisers. Bung everything you don't like in the specials class and be done with it.
The whole issue is impossible to frame without exceptions and even more difficult to police.