Hey man, welcome. By the way, I'm a fellow '79 4x4 owner. As far as getting more power out of your LUV, you've definately come to the right place. The guys here know a ton about conversions and upgrades... and I'd like to think between us all on this website there is nothing we couldn't improve or rebuild on the LUV.
Since you're new here, I'll try and give you a quick overview about what us 4x4 guys face. Unlike the 2wd LUVs, we have to take a LOT more into account when trying to get more power. We can't just slap a new engine/trans/rear in the truck. We have the transfer case, 2 driveshafts, and matching front to rear gear ratios to worry about. I'll be honest with you, chances are if you go through all that work to upgrade your current engine to something like a 2.0 or 2.3 4cyl, or your trans to a Trooper 5 speed, you won't be satisfied for long. Doing either of those involves a lot of work and cutting and modifying the driveline. If you want to do that much work, going to a Chevy 350 V-8 with a TH350 trans set up is the best way to go for added power. The 350/350 combo is very easy to find in any junkyard or donor car. Because of that, its relatively cheap to get, but then the other costs have to go into rebuilding and fabing mounts. It can get pricey, even if you do everything from building the engine to making the mounts and installing it yourself.
If you do decide to use the 350/350, you'll need to think about what you're going to do about the front and rearend. If you decide to stay with the stock 4.10 front and rear you'll still need to have your driveshafts cut and modified. Remember, as a 4x4er you need to worry about getting a transfer case too.
If you upgrade to some other 4cyl engine, you'll wish you had a 5 speed. Once you upgrade to that, you'll realize that after all that work you did, you could have had a V-8 in there. The moral of my post? If you have the money and are good with fabrication, welding, engine work, etc. then go for the V-8 swap. If not, take it from me, there is NO cheap and quick fix for a LUV 4x4 looking for more power. Get a donor 4x4 truck with the 350/350/t-case and nice front and rear ends intact and go to work, thats what I plan to do when I have some more cash.
Hope I didn't put you off too much, it was a kind of heartbreak for me when I first learned how difficult and expensive it would be for a 4x4. In the meantime, let me know if theres any questions I might be able to help you with for your 79 4x4.