EFI is way better offroad and usually not much more money.
Quite a few Chev 4.3L V6(same configuration as the Chev 305/350) swaps going on right now and there are lots of aftermarket wiring harnesses to support them. As well as bolt in motor mounts.
Don't forget that going to a V8 will require an upgrade to a bigger rad, tranny and diffs, custom exhaust, custom crossmembers, custom length driveshafts....... Make sure you budget for it all.
Buying a wrecked truck/SUV with the desired drive train is usually the most cost effective method of getting all the pieces you need.
A 258/4.0L swap is more of a bolt in and less customizing.
Chev4.3/305/350 probably the cheapest if you can fab(assuming only engine/tranny not diffs), 258/4.0L is probably the simplest more direct swap but you'll probably pay more $$$ for the drive train although you can pick up a wrecked Cherokee with a 4.0L for pretty cheap these days.
I would take a EFI 6 cylinder over a V8 carb for wheeling any day.....