Common V8 engines? What I meant by that is avoiding the "wierd" motors, if you run across them... the common ones are much easier to find parts for. GM's 305, 350, 454... Ford's 302, 351W, 460, Chrysler's 318, 360, 440. Ford's 300 straight six is a good engine too as well as Jeep's 4.0 liter.
Uncommon ones, as much as I hate to admit (it's a "pet" motor) is something like Ford's 351M/400 motor, or the very old 360v8... or finding a chevy truck with a 265 in it, or a dodge with an A engine or early semi-hemi, just stuff that didn't span decades and may have issue with parts availability both native and aftermarket.
Aftermarket parts availability isn't just for speed, it adds a whole world to how creatively you can fix something if there's an issue with the native parts. The local dealer may be gouging you $800 something for a replacement stock intake manifold on a 351W when you can mail-order an edelbrock aluminum intake for less, as an example.
Oh, and learn how to tune a carb and set points, that's easy stuff and will greatly expand the number of vehicles you'd be comfortable with... particularly points. There are a lot of beat up trucks down this way that go for pennies because the original owner let the dwell drift out of range so far the engine barely runs, and doesn't know how to adjust. One would buy it, limp it home, whip the dizzy cap off and maybe 2 minutes later after fiddling with a screwdriver and a feeler guage it's running fine.
Oh, and read up on transfer cases. Some are great, some suck, and they are on the edge of being considered a wear item (regular replacement) when they suck, and there's next to no rule of thumb as to what you'll find under a particular truck.
And don't be afraid to crawl under and give the driveshafts a shake; if they have play that's a good sign that the truck wasn't maintained as well as it might look like after a prep to sale.
