See the link to pictures in my sig regularly for picture updates of my LS1/T56 swap progress. I should be posting pictures of the engine and tranny bolted up tonight or tomorrow. I'm in the process of the swap right now.
I'm going to do a full article here when I finish as a little howto/faq type deal. In the meanwhile, I started a thread over at LS1tech.com just in case I hit some snafus, I can ask them about it over there. Here's a link:
http://ls1tech.com/forums/showthread.php?t=370781
There are a LOT of good links in that thread to articles here and there and to various photo albums of other people doing the same swaps. LOTS of good info in there. I highly suggest you hit that link
Good luck and - have fun with it. My biggest suggestions to you, if you want to learn from my experience so far:
Make sure you get everything with the engine. The big things:
PCM (computer)
Entire wiring harness
Get the MAF and airbox!!!
All peripherals (intake, PS pump, alternator, etc.)
Try to get cats/manifolds and all O² sensors (even if you won't need them)
Try to get the entire pedal assembly (clutch/brake/gas, even the hunk of firewall attached, if possible)
If you're going with a manual tranny BE SURE you ask for the clutch pedal master cylinder assembly ("hydraulic actuator") and resevoir with all lines
Fuel pump and tank, if possible
Basically get anything and everything you can get. It's better to have too much than too little. The little things add up when you gotta buy them. Example of things I didn't get and gotta pay for now:
Radiator and electric fans: $150 (eBay)
"Hydraulic actuator" master cylinder assembly + resevoir: $128 (new from my friend Bill at gmotors.com)
Shifter: $150-200 for Pro 5.0 shifter (I would have upgraded, but ...)
Gas tank and in-tank fuel pump: $300+
So, you see, that's almost $800 in only four parts I could have asked for - be wise, get everything. If I forgot to ask for the MAF, I woulda been shelling out another couple hundred. That's not everything either. I'll find more stuff as I go. Expect to pay at least $1,000 for additional parts that you missed.
I suggest doing an '01 or newer LS1, they stopped doing the EGR at the intake after '00 (realized it wasn't necessary). I would go for a 5.7L. Decide on a tranny now - 6spd or automatic - and try to get a combo package where they're coming out of a salvaged low-mileage car . Expect to pay around $3k for the pair (+/- $1,000).
ECE (early classic enterprises) sells a GenIII motor mount kit to make an LS1 directly bolt-up to our trucks ($250, worth every penny, it's superb quality, I'll have pics posted at my gallery soon).
You'll need an automatic tranny crossmember. You may need to drill a couple extra holes in the frame or xmember to use the GenIII mount kit or to get the tranny to bolt up.
You'll end up having to custom cut your driveshaft to the correct length. Any performance/hotrod shop around you should be able to do this. There is a trick to it - I have a link with more info at home. It's basically something like ... insert the driveshaft into the tranny all the way, measure to the gearbox, mark it and either add or subtract an inch from that mark to get the correct length. Again, ask and I can get you that info.
There is a great article in "Classic Trucks" magazine this month about how to convert an LS1 to a carb setup (kills the need for a harness and computer) with TH350 or 700R4 tranny. You'd need to do some extra stuff to use a newer tranny with it. Seems like a good deal, makes for an easier swap.
There's my 50¢ on the topic.