If you decide to upgrade to diodes instead of the selenium stack rectifier, you're going to need to know how the alternator stator is wound- - - -either "wye" or "delta" configuration. There's a different diode circuit to rectify each type of winding. Most (but not all) alternators are 3 phase AC units, and they require 6 diodes to rectify all of the phases to produce a stable DC output. That was "automotive electricity 101" back when I was in the teaching business, but it's been many years since I've gotten that deep into alternator theory and servicing!
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!