Yes the Magnum block is nominally .015" shorter.... 9.585" vs 9.599" or 9.600". Performance pistons will be the same pieces, ending up at a different deck height. One rod type is a bit wider at the small end, where the pins go through the small end and piston. So some rods have to get ground a bit thinner at the small end to fit between the pin bosses of certain pistons. Not a big deal.
Heads are different but interchangeable with some limitations, and the Magnum are all roller cams. IIRC, damper weights and flexplate/flywheel weights are different too. Probably more stuff that I can't think of right now.....
