For the most part most parts are interchangable. Here's a few things that aren't.
Front blocks: pre-99, 2k+, weirdos (karnivor, 05 prostock/superstock/black magic, VF-Tactical are each unique to themself), and mini. This will effect the block itself and the banjo bolt
timing arms: full size and mini
pump arms: full size, mini and midblock (and I guess midblocked and mini)
back blocks: p-block, full size
valves: standard valve, 11/16" valve (found on trillogies, 05 Black Magics, merlins, etc...)
bolts: pre-99, 2k+, evo/p-block length
I'll probably think of a few more...
As to the mechanical frame.
slider: belsales and benchmark are my favorites
hinge: dye, eclipse, ans 90, wgp hinge are all my favorites
if pump: CCM 86 is very nice as well as their 45
As to valves: any later model WGP is just as good as anything else really.