Are pre-64 Winchester Model 70 Featherweight barrels identical to pre-64 Winchester Model 88 barrels both in profile and in threading?

No.

I did rebarrel a Win M100 with a Winchester push feed M70 featherweight barrel once. That was identical contour and threads, I just had a little bit of machining of the tenon face and dovetailing in the gas block. It worked pretty slick.