I'm pretty sure nobody actually answered motorheadmike's original question. It's a bear of a question, and there are only a zillion websites you have to read before you're actually ready to ask a question. Just figuring out which cars/trucks have aluminum blocks will make you crazy. I'm going to go way out on a limb and timidly ask a question about a donor.
My local Craigslist often has (mostly pickups/vans/Tahoes/etc) in the 1999-2007 range with less than 200K and nonfatal defects (bad trannys, blown head gaskets, runs with unknown engine noises, etc.) for $2500 or less. 4.8 to 6.0, 2WD or 4WD. Most have decent bodies and mechanical stuff in sellable shape. It seems to me the unmolested engine/trans with computer and wiring are well worth that kind of money for a Gen II swap with great potential.
Do I need to read another seventy-leven web sites before I ask for more help?
Cheers - Gary
Edit - I'm enough of an engineer to buy HP Tuner and do my own wiring.
Edit2 - My goal is 375 HP or whatever I can get without buying any third party sh*t that costs over $500.
Edit3 - Just to be clear, that $500 is for goodies; I'll spend whatever is needed to get the engine and transmission working properly. I'd anticipate getting whichever stock Gen III+ used valve train parts will meet my goal, for instance.