Common tire size in the seventies

[banno]

Hello all,

I need your help: I don't want to use on my 1965 C10 the original wheels with the 6.70 tires. No problem in the USA, but in Germany it is no longer street legal to install bigger tires than the original, on a classic car (max. 2 size bigger are allowed).
Sole exception: If I could demonstrate, that it was a common practice to install bigger wheels (within the first 10 years after the initial registration), then the German technical inspection agency (TÜV) will turn a blind eye.

So, now my question: Has anybody old magazines, brochures, parts catalogs or pictures of the early seventies that could help me?
My goal is to legalize minimum 235 (better 255) tires on 8x15 rims.

Thanks in advance

Greetings from Germany