Federer has no significant height advantage over Sampras; he looks a bit taller in some pictures because he has a full head of hair while Sampras is balding in a hurry. Even then, in some pictures they are dead-even in height.
I think Sampras had a big frame like Federer also. He had broad shoulders, a massive right forearm (and normal looking left forearm unlike Federer's), and muscular legs. All in all,he had more muscular definition than Federer did so I'm sure he weighed more than 170.