When is it too much rust?

[M5-]

I'm just finishing doing the cab mounts on my 65. I bought all my parts from Mikes Bump and Grind. Super guy to deal with and all the parts are Triplus. The front cab mounts fit great but the rears were way off probably due to the fact that the rears fit from 60-72 where the fronts are for 60-66 only. The material on the front mounts is way thicker than the rears as well. I used some of the other parts like the inner footwells and they fit pretty good. Be prepared to do some forming to get everything to fit.

M5