Your 1990 uses a Delco CS-130 with an internal regulator. These are usually quite easy to find "high-powered" internals for, with only a little effort. Also, you can talk to a local shop that handles rewinds, and they can probably do the job for you for a nominal fee.
If you can't find anything locally, I talked the shop I use into doing mail-order a couple years ago, and people here have been happy with his results. I made a page for him on my site - link to my site in sig. You'll deal with Rod directly.
Note that, if you upgrade your alternator, you'll want to seriously consider upgrading your wiring as well. Another potential pitfall is that the OEM circuit has a fusible link in it - which is good for about 85-90A. If you go larger (no reason why you can't,) you're eventually going to need a bigger "fuse" as well. Pillage around on the rest of my site for information there...
N.B. You can upgrade your alternator without upgrading your wiring - and have it last a good long while. The alternator doesn't always generate full rated power - only when the regulator thinks the system needs it. However, the first time you swing to full output, you're probably going to blow your fuse...
