it could be a good idea get an acc or ign1 juntion for some functions depending on your plans for your truck, Dunno on trucks, but E bodies and 71/74 B ( and I think laters Mopars too ) got a buss ( male prong ) for Acc source embosed on fuse box but unfused. Also got a batt buss there, both visible here:





Otherwise also got a fused acc source hanging out on the harness on bullet kind terminals.

About alternator, if you wanna go for cheap on stock form, no less than 80 amps alt used on mid 80s Mopars ( they use to source 45-50 amps iddling depending on pulley diameter ). They use to go into the $50-70 rate. Other options ( on stock form ) comes from TuffStuff guys. When I get money, I'd go for the 100 amps one, but they are rated on $200-250. Powermaster got a nice stockish option too claimmed to be able to source 65 amps while iddling. Then after that there are several nippondenso alternators what it works like originals, on same stock reg and wiring.

about ammeter, since you have the cluster out, please take your time on check internally the ammeter just to be sure studs are tight INTO the ammeter shunt, not just at cluster housing,