They used the same voltage regulator for all of the factory equipped alternators into the 90s, I remember my 89 diplomat had that same regulator even though it had the same alternator as my sons 89 ramcharger, which was controlled by the computer on the first efi/TBI trucks.
( No more computer or efi on that one anymore, we retrofitted it with an 87 harness and a 4bbl)
They used that same regulator on the Cummins trucks at least til 94-95.
And those newer alternators put out more amps when called for than anything Mopar used as the alternator when they first started using that regulator. My biggest worry about the regulator is that you don't get a newer offshore made version.
Those ARE garbage.
I have a few of them I bought from eBay a few years ago, brands like Sorensen and niehoff that were popular in the 60s/early 80s stashed for my spares
That square back Mopar alternator was used til about 1987, as was the monster size 100a they had.
The square back over the years could have been anything between a 37a and 78a. Otherwise besides the possibility your unit still had its tag on it, which can be looked up as to the original rating, they all looked identical to each other except for the late model 78a, on all the rest the windings were the same width, about 5/8" or so that could be seen between the case halves. On the 78a (which 1 think also had a slightly smaller diameter case) there's a gap between the case halves where the stator is that's about 1/4" and the windings/stator is "less obvious".
