Hi, can someone please tell me if I can put the engine from an 84 2wd wagon into an 81 4wd wagon? Would this be a straight swap or are there necessary modifications (even minor ones)? Thanks!

The swap you're planning to do isn't that bad of one at all. I would recromend just swapping the longblock and reuse the intake, carburetor and distributor form the 81 that you have, those items are different on an 84. Also a 84 engine will have on each exhause port a piece of the emission system that you do not need and you will need to get them off before your Y-pipe will bolt to the engine correctly.