Hmmm, not sure how much difference there is between the V8 in you '87 and the NAS Defenders, but Wrangler Power Products did carry 120,160 and I believe 180 A small case alternators that would fit the NAS Defenders.
Not sure about the belt situation, but I had a 160A small case alternator from North West Power Products on on older Pathfinder, and it was driven by a single v belt without issue. And yes, even at full draw (it would put out about 110 A at engine idle speed per the mechanics load tester that didn't believe it could till he saw it)..
Looks like the have a 150 Amp Alternator (105 a at idle)
150 AMP -- 1993-97 LAND ROVER, DEFENDER
This Wrangler NW Power Product High Output Alternator Kit has a rated output of 150 amps. Idle output is rated at 105 amps.
Features dual fans for superior cooling. Internally Regulated Alternator Kit (shown) P/N: 200-700