Yea, the 4x4 conversion on a BII is stupid simple, unlike a Ranger. Change one axle pivot bracket, add a real front axle, swap a real transfer case for the dummy, put a front driveshaft in, pull the plug for the t-case down and plug it in. You might have to add lights on the dash for the 4x4 though. The slots and all should be there, just no bulb. My choptop is a 2wd converted to 4x4.
BIIs are well balanced enough that they do perform really well in 2wd. Other than off-roading or playing around, I almost never used 4x4 on a BII even in the winter. They go that good.
Rear springs may be sagged out, it's a common problem with BIIs I'd look more for rust in critical areas (around the hatch, radiator core support, body mounts, etc). Test drive it and then pull the oil fill cap off and see if it has a bunch of stuff that looks like snot clinging to it and a faint smell of antifreeze. Basically all the normal things you check over when you buy a RBV. 90's got the better heads on the motors though.