Well I haven't any personal experiance with mechanical roller lifters, and honestly this is the first I ever heard of any problem in a SB Ford. FE yes, but not SB. I'm sure there is no problem with hydraulic roller lifters in the SB Ford, as the factory installed them for a decade.
In terms of HP, the roller lifter has a big advantage in that it can ramp the valve open and closed quicker, which yields more time that the valve is completely open. So for the same duration as a flat tappet, the roller cam will flow more air, thus more HP.
As for hydraulic lifters, they have come a long way. The old problems of pump up was ususally weak valve springs and too thick of
oil anyway. Plenty of engines are running 8000+ rpm with hydraulic lifters. Some special lifters advertise that at low rpm they blead down and affectively reduce the duration at the valve, which is supposed to give better low rpm torque than a standard lifter.
Just some things to think about before you leap.