The alternator I pictured is a 10 DN used on 67 to 74 gm vehicles specifically our
trucks. They use an external regulator as the OP states that he has. Converting to an internally regulated alternator 10/12 SI is very easy, or even up to a CS style. I've detailed the conversion many times her on the forum.
The internal regulated alternators do not require a separate ground like the one I pictured since the regulators are grounded to the alternator case. Grounding is managed just by bolting the alternator to the engine block with clean mounts of course.
The instructions in post 12 by Wrenchbender Retired, will full field the alternator, and a voltmeter connected as instructed should give a reading of up to 16 volts. The small D shaped hole in the 10 dn will also full field the alternator if a small screwdriver is inserted. Only do this for short periods less than 30 seconds, because it will overheat the alternator. Also it may over voltage and damage any loads in the circuits, so do not rev the engine with any lights on and do not rev the engine if the HEI distributor has been installed. This especially includes any digital goodies that are sensitive to over voltage.
Pictures of the 10 and 12 SI alternators.
