Most if not all GM/Delco alternators from that period are 3-wire units; but still have an internal regulator. One of the wires drives the dash lamp (a very worthy function IMO), the other is the 'sense' line from the battery. What the "one wire" aftermarket versions do is ignore the lamp output, and internally jumper the sense input to the output.
But frankly, the wiring is pretty trivial. Buy the plug to go into the alternator (available as a repair piece at FLAPS) and splice two wires; now you have a "wiring kit" in your hands. Terminal 1 is the output to the dash lamp (some alternators require that this be hooked up or they won't work), Terminal 2 is the sense input. Numbers should be clearly marked on the alternator housing. Here's a random image from Google:
You didn't say what alternator you have now (or I missed it). There are "rebuild kits" available for some of the most common units (like the 70's Delco) that usually include new diodes as well as brushes and bearings. But often the diodes have to be soldered to the windings, so check out what you have first. Just for an example, here is a 12Si (70s GM Delco) kit on eBay
https://www.ebay.com/i/141976219938?chn=ps&dispItem=1
I went with the externally regulated Ford unit "back when", as it was very slightly smaller than the GM unit and space is limited. Had some shortcomings, like the alternator had to come completely loose to change the belt; but it served me well for many years. I grabbed the alternator, regulator and harness from the junkyard (68 Mercury Grand Marquis IIRC). I did eventually replace the original mechanical regulator after it failed with a more modern electronic unit, but it was a drop-in replacement.
Here's a shot where you can see the alternator and it's regulator.