OK, I did a quick look at my 87 and my 91. On the 87 (first pic) the belts seem to be a bit longer, so the square threaded block sits farther outboard so away from the pulley.
On the 91, the square block sits farther inboard, so it's actually behind the water pump pulley, but there's about 2 mm clearance in the fore/aft direction. Not much but enough I guess. The nut to tighten the adjuster sits fairly close to the pulley too, but it's outboard and below a bit. Second pic. 3rd pic shows belt size on the 91. Hope that helps! If your lower bushes are not in good condition, then the whole alternator can skew a bit which would make things worse. Also, make sure there's no washer between your upper bracket mounting and the block mating surface. I assume your upper bracket is the one that has a large tube with a round flat "washer" welded to the back side of it, and the bolt goes through from the long side of the tube into the block. There may be a washer on the front side, but you shouldn't have anything between the bracket and the block mating surface. Also, the bracket should be perpendicular to the block - if it's bent forward at all it will reduce clearance to the pulley obviously. Hope that helps a bit.
