Jimbo these bike were around, and yes all that matters is the rule states as in any class if it was raced in the "world" pre 75 its also deemed OK, based on the fact we had dirt track for a long time anything with the year cut off is cosha, included MX bikes which are hardly Dirt track just because you change the rear tyre, or other wise it should have been called speedway, so i think your just off target there.
But i do agree on the other stuff, as far as im concerned all that programable stuff is Outlaw, moreso from the outside the bike should look as it did when it was racing in its period, uder the current rules you could put a 2008 motor inside 74 cases, but thats not really in the spirit of it i think, and after all its about the bikes, capturing a period for what it was, not for what it could have been, you want to race a bike like that, simple just ride a modern, if you wanna build a custom for your own enjoyment and building skills go for it, but you wanna race it against others in the spirit of a time capsule, go easy on the mods and the 2000 technology, i cant see the point of transplating/creating a new bike onto a classic frame and to think its going to be a reflection of the period or in the spirit of classic racing.
There are boundries, some cross them for there own reason, others learn its not all about winning a plastic trophy its about enjoying.