The "button" diodes (3 of them) are pressed into the deeper recesses of the aluminum rectifier heat sink in an alternator. A better choice for cutout mod is a stud mount type with heat sink compound for better heat transfer to the bus bar. Diode should be rated at least 25A. Use 12AWG for connection.
Example for negative ground -
https://www.ebay.com/itm/50-AMP-100...IODE-Rectifier-POWER-SUPPLY-50A-/121864495540
Positive ground type also available from the same seller.
Example for negative ground -
https://www.ebay.com/itm/50-AMP-100...IODE-Rectifier-POWER-SUPPLY-50A-/121864495540
Positive ground type also available from the same seller.