what cross member you talking about, for the trannny? that may be different. if you plan on changing the transmission. most of the time you can move it back or forward if needed. should be extra holes drilled in the frame.

for the engine mounts most of the time you need V8 mounts for the K frame up front. so the V8 engines fits.

and you'll want new springs for up from, the v8 may make the front end take a nose dive due to the extra weight.