Where to buy correct alternator for a 1969 340 swinger non a/c car

Oreilly shows both single and double pulley round back 55 amp available.
Sure, if you want so-called "remanufactured" garbage with a lifetime warranty that means you get to spend your lifetime exchanging dead parts until you finally give up, and if you're gullible enough to trust that when they say "55 amp" that's what you're getting.