How much original frame to be legal?

With all of these bike threads sprouting up it gets me thinking, how much of the original frame/bike do you need to keep to stay legal?

Can you just cut the head tube (w/vin) and weld whatever you want to it and title it without problems down the road?

The vin needs to match the registration and you need to follow all laws by that year. My 58 is no where near factory. No tach no speedo I won’t be running a front brake.

so I can buy a mid 90s kx125 and put basically everything from it onto my 72 f7 and it’ll be legit?

as long as you have an original neck with matching papers, you can do whatever you want behind that, and as long as it has 3 or less wheels it’s considered a motorcycle and it’s original title is still valid.

yeah but HD didnt start using vin stamped frames until 1970.

hmm. interesting…