Wow what a cool thing to have in the garage!
If cutting and shutting is allowed, then it’s allowed… but if it’s not, then it’s not. That’s what I mean about it not being complex, just read the rule book.
But…are you sure it was allowed? Or did they just get away with it? I know of one prominent Norton racer (who shall remain nameless, but SteveA knows him) who told me they played around with different diameters and lengths and cut n shut them to tuck them in, he also gutted the peashooters to modify the internals, but by his own admission this was all “not quite strictly within the rules”!