A friend of mine recently gave me an externally regulated Delco alternator, "just to have a spare". It was given to him and he didn't know what it was out of.

I didn't think much of it until I noticed that the cooling fins on the fan faced the opposite direction from what I am used to seeing. When facing the alternator, the fins are set up for rotation in a clockwise direction. Also, for what it's worth, the fan and pulley are a one piece assembly - not two separate pieces.

Any idea of what the application could have been?

The crankshaft rotates clockwise as viewed from the front. The alternator would turn the same direction as the crankshaft--clockwise as viewed from the front/drive end. Sounds like a normal-rotation alternator.

Some manufacturers installed the alternator facing the engine--Honda did that for awhile--so the alternator spins opposite crankshaft rotation.

Seems to me that the main difference between a clockwise and a counter-clockwise alternator is the fan. Change fans and you can change direction.

sounds like the fan is off of a corvair. Alternators will charge in either direction. The fan is for cooling, drawing air from the rear of alt. A fan for the wrong rotation will not cool properly, but will still work till it overheats and fails. There are also bidirectional fans, that will work in either direction.