Here's a sad story about rebuilt alts. I have an 83 22r, alt went bad so I took it to NAPA auto parts for an exchange. They checked it out, took the numbers off of the unit and gave me a replacement.
The moment I fired up the truck, all hell broke loose. Alt and brake lite came on, then total failure of the entire electrical system. Every fuse was blown, all lights were blown (bulbs actually broken), fuseable links melted, etc.  Unregulated power surge took out everything to do with electrics.
NAPA had given me an 'A' type alt and mine was a 'B' manufactured in Canada.  I told the counter man that this was a Canadian built truck and things may be a tad different. They later claimed their computer program was in error.
It took me three weeks and 500 bucks to get back on the road. When I turned to NAPA for a refund on expenses, they had changed the computer program and told me it was my fault.  The store owner refused to to pay up!
I have not stepped foot into a NAPA store since and never will again, they suck.