I did a parts search on AutoZone for an 88 V6 and an 88 L4. Search results showed different part numbers for the alternators.
If you're thinking of replacing the alternator, be sure to compare the pulleys. Count the number of ribs on the pulleys before you hand off your core. I've encountered pulleys with 1 less rib on a number of occasions involving GM cars, including a Fiero. Someone also recently said their pulley had an extra rib so the pulley was wider. Probably not as bad as one that's too narrow. It will shred a new belt in short order.