The full load ammeter setup is not the weakest link really but the bulkhead. Aside ( IMHO as I have mentioned since ever ) the low rate charge alternators.
After 40 years of abuse, maybe the problem with your ammeter was the studs loosen from the internal shunt inside, which are pressed in. The heat produced due the poor electrical production made by the STOCK ALTERNATOR ( which is the first and initial guilty on this, being underrated ), stretchs out the shunt making the studs get loosen. You can fix this simply get them tight back to the shunt or even welding them to the shunt. Myself fixed a 70 Charger ammeter simply welding with lead and soldering gun. But after this you need to take care about the bulkhead conditions, upgrade accordingly, but FIRST AND PRINCIPALLY, GET A PROPPERLY RATED ALTERNATOR FOR THE CAR LOADS NEED, to get the battery out of the game as much as posible, for both situations, charge or discharge, getting all the loads playing just on alternator side of the game. This will get you an ammeter practically death centered, meaning no loading going throught. No load there no heat.
Then since 75 ( 76 on A bodies ) Chrysler allong with the rest of the automotive industry applied a new technology, using a remote reading ammeter, which doesn't get loads going throught, but just a partial and minimal load, amplified by a coil mounted on ammeter to be able to move the needle. This cars were wired way different than the full loads ammeter cars. Was just a move forward on technology, like the electronic ign and regulator systems were.
However a full load ammeter can be still safe if you understand the system, make the propper mantenience because 30, 40, 50 years are not a joke on them, specially after wiring incorrectly some extra accesories or using the incorrect battery rate but still keeping the low rated factory alternators. All of these together got an unecesary stress on them... for all these years.
Every body gets serviced their carburetors, but nobody gets serviced the electrical system. Sometimes it's handled and "tricked" up to the fail comes. Then blame the ammeter, LOL