The SEV alternators aren't the most reliable alternotors going around. 140 carb car gets 35 amp, injected gets 55 amp. Not sure about 164S, but 164E certainly gets 55 amp. The rear of the alternotor has the red diode bank bolted and soldered on to the back. For whatever reason a D+ post passes through and the the wire is bolted to it there. There should be a plastic tube insulating the post from the dioded and also fibre washers are used to keep it insulated from the D+ post. Follow the greenbook closely. If an alternator is charging correctly, it is working 99%, so your first one is close. If it charges at 13.8 to 14 volts at any speed above 1500 engine rpm, then the regulator is working.

Failing that, converting to a commonly availale alternator is the way to go, but requires some talent. I use the local made in Australia Bosch alternator found on nearly all Australian cars in the 70's. I like to get one from a Cleveland because they have a big pulley for some underdrive.
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69 142S Overdrive + 69 164S Manual