The motors are about the same weight. Just buy some new '56 V8 springs and you're in business. Lots of places will have them, but if you have any trouble, these guys are the pros......www.eatonsprings.com
Be sure to inspect control arm bushings, ball joints, tie rod ends, etc. while you have it down.
Oh, and by the way, 56's came with 265's, not 283's.