Old thread I know, but I wanted to share what I did on my '84 BII with a 2.8 a few months back. I don't know if I got this idea from wildbill's post or if I saw this elsewhere but I sourced a GM alternator spec'd for around an 84 Chevy pickup/suburban, 78 Amp for $61 shipped from amazon, no core charge. You can also source a 63 amp alternator for less, I was able to find a lifetime warranty one at a local autoparts store for $50 ($35 for one year warranty, reman)
The only alteration to the stock mounting is a 1" spacer needs to be put in place on the rear of the lower alternator mounting. I had a piece of bar stock that I drilled a hole in to make work.
The advantage of this GM alternator is easy to wire and cheap, (way less than the Ford 3G alternators people talk about) plentiful alternators should it ever go out on you. Every autoparts store in North America will have an alternator in case you find yourself away from home with a dead one.
Wiring is pretty simple, instead of an external regulator, these have an internal regulator with a three-wire hookup. After having both three wire and one wire alternators, the three wire is just about as easy to hook up and performs better than the one wire. The one wire alternators were mostly meant for special applications besides automotive uses: think generators, tractors, boats, etc. The three wire uses a charging wire, a sense wire and a turn on wire, easy enough to wire and it better responds to the variable load put on the charging system of a vehicle: blinkers, windshield wipers, stereos, etc.
