voltage problem 74 duster

That is whack..

any more history on the car.
like why did it have a new alt put in?
or Did the guy wire all of the new electrics correctly?
Some of the most hellish electrical problems come from one little thing that takes out the whole system. One little thing wired wrong, or too much load for the system or wires. (don't forget that the wiring in the system is just as important as the other components.)
I could go on and on..sorry