Most likely a lot of difference. Prior to 1995, only the SUV's got 4 wheel antilock (4WAL); pickups got rear wheel only (RWAL). The older 4WAL units were huge Kelsey-Hayes units with an external combination valve (proportioning valve and brake warning light pressure switch.) In 1995 pickups went to 4WAL as well and it's a much smaller fully integrated unit. I am about 99% sure you can't swap them.
With that said the old style 4WAL units are pretty problematic once they get old. You didn't mention your symptoms but if it's just unexpected ABS activation then be sure your sensors and tone rings are clean. If that doesn't solve it then have the system scanned. Not all scanners can read the ABS unit. If you get a whole pile of codes related to the unit itself, it usually means it's bad. Sometimes it's just grounding issues but I think those are the minority.
Richard