Three wire alternator on a two wire system?

... I wasn't sure how to look it up since I assume when I tell the site I have a '68 it will just give me a part number for the old mechanical voltage regulator.
That ebay one will work, especially if you want to pay more to get the original "big, black box" look.

Why do you need to ASSume? This spoon-feeding took me 30 sec:
rockauto, 68 Barracuda 225, $24.
I could swear I only paid $11 a year or two ago.

And you shouldn't call your car a "cuda". The early ones were A-body named " Barracuda ". When they changed to E-body, they were renamed " 'cuda ". For slang, call yours a "fish".