Yeah, that ammeter looks like it's well done
The truck's wiring connects the ammeter in parallel with the main feed / charge wire that runs from the positive battery terminal, across the radiator support, to the bus bar (2 screw terminals) on the horn relay. So that main feed / charge wire serves as a shunt for the ammeter. And the shunt wire normally caries nearly all of the current with only a small fraction taking the parallel path through the meter itself. But in the event of a bad connection at either end of the shunt wire, all of the current tries to go through the meter, causing damage like you're seeing there. Sometimes the black & black w/white stripe wires that connect the ammeter get damaged due to excessive current too. To prevent that from happening, I recommend adding a couple of 4 amp inline fuses to those wires like GM did in the 67+ trucks. Put one fuse in the black wire that connects to the "batt" terminal on the starter solenoid, and the other fuse in the black w/white stripe wire near the end that connects to the horn relay.
Edit: just saw your post on the oil gauge. Once you install the compression fittings onto the line, they can't be removed again without damage. But the line / fitting assembly can be connected, disconnected, and re-connected to the gauge a few times as long as you're careful not to over-tighten the fittings. You might also want to double check to make sure you have the correct fittings. The originals used special compression sleeve nuts (Weatherhead #6100x2 or equivalent) where the ends of the nuts have a built-in compression ferrule. The ones you have pictured appear to have separate ferrules ... they might still work, but it would probably be a good idea to make sure they thread into the back of the gauge okay before permanently installing them onto the line.