What the H#!! is this noise? Slant six mystery engine sound...

Oh yeah, that just eliminates it from ANY and ALL possibility. LMAO
Well, all jokes and sarcasm aside, your asinine comment tells me you apparently overlooked my other notable comment about the alternator. I did spin it by hand while I had the belts off, and while it isn't the same as the mechanical load provided by the belt from the crankshaft, I found no perceptible play in the bearing--thus lowering its priority on my list of possible noise sources.

Don't think I'm too stupid to recognize the possibility of a part being broken out of the box. Rather, I used common sense to downplay its likeliness as the noise source since it's the only new pulley on an otherwise-original 40+ year old accessory drive. Thanks A TON for the constructive comment, though.