There's too many variables to predict the outcome of such a setup. Minute differences in chainstay angles, brazing of drop-outs to chainstays, drop-out type, hub spacers, cassette lock rings, original spacing and whether it has been set, etc.

That said, I have a 1985 Look 753 frame that, without cold setting, seems made for Campy 10 speed with an 11T small cog. A Merckx frame of the same vintage is maxed out by Campy 8 speed with a 12T cog.