I would use the ls crank and rods in the gsr block. That way you wont have to do an lsvtec conversion and you can use the factory oil squirters. Using the LS crank will give you more tq due to longer stroke than the gsr. As for what fasttech said about the blocks, he is wrong. As long as you use ls rods with ls crank and gsr rods with gsr crank you will be fine. B16 pistons will be a nice setup since it will get you around 12:1 cr. The difference between the 2 kinds of b16 pistons are only like .2-.3 points of compression. If you do this setup be sure to get arp rod bolts if you want to safely rev to 8k+. Also if you do b16 pistons just bore the block since 81mm pistons are easier to find than .25 over. Afterwards get it tuned if you want it to last.