One thing I just ran into. I put a 90 amp maxima alternator in a couple of years ago. My charging during the summer was always marginal. I'd have to thow a charger on it at least once a week. This summer I decided to do some checking. To make a long story short you cant run 90 amps of power through a system built for 45 amps. The route on the factory wiring on my 73 is alternator, amp gauge, fuse box, Fusable link, starter, battery. I added an extra 10 gauge wire from the alternator to the battery and the problem has gone away. Obviously the amp gauge isn't accurate anymore and at some point soon I'll be doing a major rewire job.
Derek