None of the U.S. gen 1's had disc brakes that I'm aware of. There were disc brakes available for the Aussie and UK models (Pajero) but shipping on those parts is a pain. The other option I have looked into as I personally don't want to do a full axle swap from a second gen is to check the bolt hole pattern on the second gen rear disc brake caliper bracket with that of the first gen to see if they match up. If that were the case the a rear disc swap would be a bit more viable. One thing I have read in other posts is that the V6 did have larger front discs than the four banger and the second gen had larger calipers than the first gens which bolt up to the same caliper bracket (posts on both) as well as the upgraded suspension ie. rear trailing arms, rear coils, rear sway bar, and front sway bar.

Do some reading. The guys in here have provided a wealth of knowledge, ideas, and experience for the benefit of everybody.