from the questions you're asking, i would say you need to do a ton more research before you even think about a swap like that. unless you're not worried about the cost, i'd forget about the crate engine and look more for getting a complete used engine, maybe off ebay or a junk yard near you. as long as you get an engine that is newer than the 84 you're putting it in, it shouldn't be a problem... however, make sure the engine is a california engine.
as far as what you'll need... you didn't mention your drivetrain, but unless you just plan to do light trail riding, a tranny swap is probably in order. new motor mounts, radiator, exhaust, if you swap the tranny an adapter from it to your tcase. all in all not cheap to do, nor easy, no matter how you look at it. also you'll need to pull the wiring harness and computer from the donor engine and send it off to a mod shop... there are several advertising on ebay... and they'll send you back a stand alone wiring harness that just has about 6 wires, starter, etc. and is programmed for your application.
a quick run down gives you an idea of the cost here
(5.3s are generally plentiful and not that expensive... for all out sickness factor, an LS1... actually if you find a decently priced LS1 with low miles, just step away and email me...)
5.3 engine $2000 or so w/ tranny, engine itself 1kto1500
tcase adapter $500
aluminum radiator $500
wiring modded $300+
i would budget it at $4000+ as a rough estimate, leaving room for the unforeseen. of course considering you're only paying $500, that would be a pretty sick $5000 dollar jeep. that doesn't take into account your mechanical ability to do it, or the cost of labor if you need to job it out. research, research, research.
take it easy,
00 Lexus GS300
97 Suburban 6.5 Turbo Diesel 6" lift 35" BFG A/Ts
81 CJ-7 rock buggy, injected 350, built th350, 3.8 atlas II w/ ebrake, d60 front 1.5 stubs w/ detroit, 4.88 gears, discs, d70 rear w/ detroit, 4.88 gears, discs, 37" krawlers, 17" trailready beadlocks, 16" king coilovers, 4 link f/r, 12+ point cage, howe full hydraulic steering, fabbed by owner :D