I did a complete electrical upgrade over the winter, going to an externally regulated CMI 105amp alternator. I have two of the original OEM 51 amp Prestolite/Leece Neville 2017KA alternators for sale.
1. The one original to my engine was cleaned by an alternator shop and bench tested as putting out the required 51 amps.
2. The second I bought as a spare from another forum member, which I also had bench tested and it too put out the required amps.
Both are in good working condition and fit my Universal 25XP engine. They have 3/8" pulleys.
$75 each + shipping.