Don't get distracted by the Delco-Remy alternator
(which is not Delco, or ACDelco) they can be plenty good. The fact that is it Westerbleak Red means it was original to the engine in all likelihood. Video stops at 3:15 into the run, here.
The diode could be a zap-stop, or a kludge to a one-wire conversion, but the fact that it is simply hanging in the air and not secured to any solid surface means it is probably NOT original to the engine. Unless WB did their usual Looney-Tunes design work.
Delco-Remy WILL answer phone
calls, and I'll bet they'll tell you the alternator
should never have been painted that way, either. They'll certainly be able to tell you what that diode is about, they are engineers and businessmen in the best old-fashioned sense, who enjoy talking tech and educating their customers.