The only "straight" swap is a G series Suzuki - anything else will require faffing about with adapter plates, mounts, etc. - swapping in a larger G series does require the adapter plate etc., but it is so commonly done that they are readily available kits.
You can swap anything you want in there, but the more radical the swap the more work is involved and the less your chance of pulling it off successfully.
One last thing - any gasoline engine can be run with a carburetor - they don't care how you mix the fuel & air, just that you mix them in the appropriate ratio - again - the more radical you go, the more work is involved and the less your chance of success.
The most common swap into a Samurai is a G16 from a Sidekick and like I said there are kits available, there are also kits to drop a V8 or V8 in.