Re: v8 swap " Life IS Good!"
My CJ had a 2.5L AMC in it originally. I was getting 12-14MPG avg I bought a 2000 Vortec 5700 V8 engine that basically is what you'd get in a Suburban, C/K series pickup or a Van. My CJ now get's 19 to 21 MPG avg. I recommend buying the entire vehicle if you use a junkyard engine so you have all the small things that you may not think about up front if possible. Stock axles won't in most cases be adequate for the swap and will need to be addressed eventually. Make sure you get everything on OBD II vehicles including the exhaust system for the up/down stream O2 sensors, catalytic converters and computer. If going with an automagic transmission, unless you have a long wheelbase Jeep such as an LJ Unlimited, CJ-8 Scrambler or CJ-6 Jeep, id avoid the 3/4 & 1 ton 4L80E because you will have a very short rear driveshaft and on a CJ-5, it's not even really possible. The 4L60E is great for wheeling and is short enough you can use it in CJ-7 YJ & TJ's without much trouble. There are cradles or engine mount adapters to install most common V8 engines and if you own a CJ, you might not even need any adapters depending on year etc. Some Ford engines convert well like 5.0's depending on transmission if you're trying to keep a Jeep manual transmission in your vehicle.
As far as what's best for you as a donor depends on what year Jeep you own and if you have to worry about the smog nazzis coming down on you. Generally if the year of the engine is newer than the vehicle and it has all smog equipment that was required on that year, it can be made to pass in most smog states.
Example is my 85 CJ, the motor must be equal to or newer than 85 and must have at least the smog equipment originally on an 85 light truck. If it has a newer engine and the newer engines car or light truck emissions, it will pass. However, if I tried to put a 1963 engine that has no EGR, no PCV valve, no air pump, no cats, no evap canister, has a road draft tube and an oil bath air cleaner, that would not pass obviously. If I put a Diesel engine in my CJ, it would exempt it from further inspection and that would be cool but I couldn't find a 4BT for as cheap so I went with plan V.... As in Vortec. As far as whats right parts wise, CJ's are easiest to V8 because they came with them new at one point so it's easy. Wranglers require a bit more work but YJ's are actually real easy especially pre-EFI 1991's. You will have to most likely change the transmission and that in turn will affect the T-Case and driveshafts plus you may blow up your stock driveline anyway if trying to use it with anything more than 28" tall tires. I know because I had to eventually put 1/2-3/4 ton axles under my CJ so they would live for more than 15 minutes. So one should budget all these factors before ripping the engine out because one change begot another and another down the line if you know what I mean. I am glad I dumped the 4 banger and doubled up on the number of jugs under the hood and if you ask would I do it again? That's a NO BRAINER!
In my case the net results:
Horsepower went up 2.5X
Torque almost trippled
Economy up 5 MPG
The all important FUN FACTOR Up 10 fold
One of the 7 wonders of the wheeling world: To drive a V8 powered short Jeep!
Cost: $800 Vortec Engine with 4,000 miles on the mill including sensors, computer & wiring
M.O.R.E. Bomb-Proof motor mounts $225
EFI miscellaneous stuff $300
$250 for the clutch kit and flywheel to fit the V8 engine
$180 for the new 33" TSL's after burning off the first set of BFG's in exposition 4 wheel burnouts
$LOTS$ for the replacement axles to handle the power after blowing up the AMC 20 four times!