I am in the process of doing the same swap. I'll see if I can chime in here what I've found out:
There are two companies that sell "install kits" for LS1 motors:
Street & Performance: www.hotrodlane.cc
S&P makes a motor mount, which sets the motor further back, you can re-use your stock accesories but not the AC, you'll either have to notch the subframe or run one of thier expensie serpentine systems. They also make a shorty header to go with these mounts and you'll also have to notch the oil pan. They sell these as well or offer the service.
BRP Hotrods: www.brphotrods.com
BRP makes a motor mount as well, which sets the motor further forward. This enables you to retain all accesories and the AC, and the oil pan can be left stock. But you must ditch your stock rear-steer and run one of their retrofit 4th gen rack & pinion kits. This requires notching the subframe and they give you instructions to do this yourself, or they offer the complete service. The sway bar is moved to the rear of the a-arms, and the main advantage to this setup (besides the rack & pinion steering) is that it enables you to run long tube headers. Now there is a company called Stainless works which sell these and they are the only "bolt-on" longtube for LS1's desgined for 1st gen's. But you must use the BRP motor mounts and rack & pinion steer. BRP also sells a T56 install kit.
That narrows down the hard install of the motor.
For the T56, like I said before BRP sells a kit, but American Touring Specialties (ATS) also sells a more complete kit: www.t56kit.com
I also think Kiesler engineering sells a T56 kit.
For wiring there are some options:
Painless makes a wiring harness for LS1's, although I think it's only for 98 PCM's but I may be wrong. You can also get a custom harness from Street & Performance or you can get www.speartech.com
to modify your stock one and re-tune the computer. The modifying includes removing Vats, Air & Smog equipment. There are various companies that can tune the computer: LS1speed, MTI etc.
For fuel is where I am a bit stumped. Most guys use these Rock valley stainless tanks: http://www.rockvalleyantiqueautoparts.com/catalog.htm
you can also buy narrowed versions from Detroit Speed & Engineering if you are mini-tubbing and running 335's. You can also do fuel cells, other custom tanks or modify a stock tank. The Rock valley tanks are big $$$. Not sure if you can run a stock tank with an external inline pump only.
For cooling you can run a donor rad and fan setuo from a 4th gen, or an aftermarket rad like Be Cool or others.
I found most of this info on www.ls1tech.com