My local alternator rebuilder has an assortment of pulleys. Try one in your area.

FYI, I had a custom 140-amp alternator made here in Vegas that I bolted into my 560SEL. He put a single belt pulley on it but I'm sure he could have done pretty much anything I needed.

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There is a very fine line between "hobby" and "mental illness."
FrankenBenz: '87 560SEC with an '02 cammed LS6 and custom 4L60E.
Bling: '87 560SEC, ported/polished, lowered
Lisa: '87 560SEL, lowered