+1 for the link to Ken Hemmings' site for a reliable unit for your '88
The only significant difference for the '88 - '89 alternator is that the mounting holes in the alternator are slightly larger than the mounting holes in the later years. The early alternators use shouldered mounting bolts (hence the larger diameter holes) and the later years do not.
To fit a newer model alternator on your '88 you can bore the bolt holes on the alternator a little larger and retain your OEM mounting hardware, or replace the OEM hardware with non shouldered bolts. For me, I prefer to bore the alternator mount holes just to preserve the design (the shouldered bolts are intended to keep the alternator from spinning on the mount, which is accomplished by sleeves in the later years).
Shameless plug - there's a
Compufire alternator for the '88 in the
For Sale/Wanted Forum on this board.