Mill decisions

W2's are expensive but if your starting fresh then it really won't be all that much more money if you go to a W2 head. W2 heads take a different manifold, rocker arms and headers but if your going to buy all of that new anyway you might as well go that route. Ported right they flow great on intake and exhaust; way beyond what you could pull from X heads unless you just completely went all out on the x head(raise both ports with epoxy.....ect.). As for strokers the 4 inch is the most popular and you can actual buy the whole rotating assemblies from many different places but most are forged and some even machined in china so have your machinist check everything. But honestly I'm not sure any of those kits will handle the hp you're wanting to run. I would call the manufacture and get their opinion before I'd buy the kits. As for the block it really doesn't matter in my books just find the block with the thickest AND most consistent cylinder walls. I know you don't want to hear it but the block will be a weak link in the build. There are many things you can do to help out bottom end strength but since you don't want to add block filler there is nothing you can do about about cylinder wall strength. Hope this helps you out and I imagine some one will chime in about your build.