There are a few differences like the speakers may be the ones on the ends and not in the center, some courtesy foot lights that come on with the dome lights, also your wipers may need to be on the column and not the dash, unless you use the El Camino bezel and wiper/lights switches.
It's not really a straight foward swap, it'll take some thinking and you'll definately need a test light. If you are using the MC harness with the donor dash, the wire colors are slightly different too.