Darton makes sleeved blocks or just sleeves that you can insert into your prepped block, I can't seem to find it now but I swear there is a 4.2 stroker somewhere, this place has the 3.5-3.7 block,
http://www.turbo-kits.com/350Z_turbo_kits.html (not the new 3.7 just an overbored block)I believe the stock internals are good to about 400whp, at which point the rods become the weak link, sleeves, forged rods and pistons can get you to 600whp before the block becomes a real issue, then you swap in the darton block and and get into real crazy stupid fun kinda power they claim 1000hp capable!