First off, don't even bother unless you are going to do an injected motor. I bought a 2001 5.3L Chevy from a salveage yard. The dude said he had 23 of them and they were all between $600-$900 depending on miles. For that, you get the engine without accessories. It was another $150 for the accessories and brackets.
I had the injectors cleaned and tested for free by a friend (for peace of mind), had the factory harness modified and bought a computer and program from a guy on E-bay for $400. You can run a Jeep 3 core radiator like the CJ V8's had or get an aftermarket bolt on for about $175 that has the Chevy outlets. You also have to get an inline fuel pump that pushes 55+ psi ($85).
There is enough room to run the chevy fan, but I opted for dual 12" fans with a shroud from a Ford Focus. It fits perfectly on the Jeep radiator ($150). You will also have to buy a K&N filter and some random tubing to run it with ($50).
Then you will need an adapter for your transmission. I was running a Jeep Th400 and scored a chevy Th400 housing for free. I went ahead and had it rebuilt for $400(again for peace of mind) and had my Novak transfer case adapter installed. You could run a 700R4 that will bolt to your transfer case.
You can see what was originally a great deal on an engine gets pretty pricey by the time you get it installed. The PRO's are that the programmer claims the engine will now make around 315 HP, it starts by merely bumping the key, should get significantly better mileage than my old 360, is a modern port injected engine and weighs less, not to mention the hairs standing up on your arms when you open the hood.
Slightly older vortec 5.7's can also be scored at a great deal.
