MustangSlayerWs6

Hey guys I would like some info on building a motor. It'd be much appreciated!!! First off I have a 00 ws6 with a ls1 6speed and it already has just minor bolt ons. I want to build a whole new complete motor without pulling the stock until the new one is done. I plan on spending around $5000 including clutch. With possible supercharger and nitrous added on in the near future without whole motor tear down again. I don't know which block to go with to start the process. aluminum, cast, 5.7 6.0 etc. with all my electronics and mounts still being the same.
If anyone has info, good, bad experiences please tell!! Thanks much