Well you can certainly fit an LS 5.3L V8 in there. And it's an aluminum engine, so it weighs nearly the same as the stock engine.
Aftermarket turbos can be very expensive when done correctly. If you plan on running around 4 or 5 pounds of boost, you can pretty much bolt on a turbo. Any more boost than that and you really should build the engine for the turbo. This would entail forged aluminum pistons (to survive any unwanted knocking that might occur), increased volume oil pump. The turbo is lubricated and cooled by engine oil that flows fairly freely past the impeller shaft. This can significantly drop your oil pressure, hence the need to install a high volume pump. Overboost must be prevented, so you'll need an inline limiter (not the best) or a waste gate (the best). Then there's the nightmare of connecting two exhaust manifolds together. Do they go under the engine (but where?) or over the engine (but where)? A cleaner install would be bi-turbo, one for each head. That eliminates the cross over pipe and, because each of the two turbos is smaller than a single turbo, you cut any turbo lag by a factor of around 4 (the angular momentum of the impeller/compressor is half that of a single larger turbo and the amount of time required to get to speed is a function of the square of the rotating assembly's moment of inertia). You could also install sodium filled valved to help transfer heat out of the engine cylinder. And what about the bottom end of the engine. The 3.8s are pretty weak.
A more practical solution is a supercharger. The install is easier but you should still do the other things you'd do to build a turbo engine. The problem with either of these solutions is that there are guys out there that, after the installation, are still not satisfied with the power. I have a 4 door set up for expedition, so it's heavy. 2nd battery, on board air, air tank, 35s, roof rack, heavy tool box I drag around, refrigerator, crap on the roof rack. It adds up pretty fast.
I put in the LS 5.3L V8 with the 6 speed trans. You have other options as well: 6.2L with 8 speed trans for example. There's no extra stuff in the engine compartment. The V8 fits almost exactly like the V6 it replaces, so even with the V8 it
's not all tight and cramped in there. I had MoTech in Las Vegas do the swap (see lswrangler.com).
