There will be a casting number on top of the heads that will tell you what they are. The pistons should be attached to the rods still, and they should have a number stamped on them for where they go... it does matter if you are reusing the original stuff. If it was bored, then the original pistons wont work as it will be a 4.25" bore PLUS whatever it was bored too.. i.e bored .030 over will now have a 4.28" bore. If they just honed it, you can reuse what you have. I got a Gen VI 454 from a 1997 K2500 Suburban with 288,000 miles and had is cleaned and inspected. They had to bore it 0.020" to clean up the bores and then got new speedpro 0.020 pistons. The pistons were installed on the original rods and then the entire assembly with new harmonic balancer and OEM flywheel were balanced. The block was decked and then new bearings, gaskets, seals, water pump, pushrods, lifters, and timing set all came in to around $2200 out the door. I paid $600 for the heads to get fully rebuilt and then $140 for a custom regrind of my OEM roller cam.
Pics will help with a lot of this. Pics of the block, bores, mains, pistons, rods, whatever you have already.