does anyone know how to clean alternator housings with damaging the original finish?

glassbeading works good with aluminum but it for sure would not look original. Not sure if walnut shells or any of that exotic stuff would be what you are looking for but here's a BTT for ya. Just me I'd clean it with simple green and a toothbrush & in your situation I would try that on a spot on another alt like one on your DD that the appearance dont matter & see how it does/turns out

Send it to Dixie restorations, and feel well afterwards

Soda blasted mine and it looks great, picture to big to post but PM me your e-mail address and I'll ship you some.

soak halves in Berryman Carb dip and scrub with toothbrush. Dont use etching acid/sodium hydroxide cleaners (like driveway cleaner) as it will turn AL a dark gray. Simple green or white lightning works well, Maybe Purple power but check that one for discoleration.

My alternator was beyond a cosmetic clean-up. I sent mine to Jim at Dixie restoration. His work is amazing and such a gentleman to deal with,

Any kind of abrasive blasting will ruin aluminum alternator housings. That's why rebuilt units can't be restored - the rebuilders blasted them.

Jim at Dixie has recently just started adding a chromate to the cast aluminum parts that duplicates the factory coating. This might be some kind of Alodine. I returned my alternator to him because I messed up and asked for the wrong pulley. He gave me the correct pulley, added the new coating, and re-tested it for no charge, just the freight. I suspect he had to disassemble and re-assemble to add the coating, but still no charge.

Thanks to all who answered my post bob horman