2.0 Silvertop was only in earlier Mondeos then it needs a 1.8 sump and oil pump and oil pick up, maybe water pump too I can't quite remember. Mondeos are getting harder to find these days.

2.0 Blacktop was in Focus and Mondeo, so there are plenty of Focus models still out there.

Plenty of ST170 still about too for the ST170 engine.

I think it all depends what your end goal is as to which one to go for. Turbo, throttle bodies, carbs, super charged, oem ecu and standard fueling and ignition control.