Which guage or both ?

longarm, I don't see any "external (ammeter) shunt" in your 1970 schematics, do you?

Again, the big red wire from the ammeter on your '70 model goes, via the bulkhead connector, directly to the positive battery terminal at the starter relay. The big black wire from the ammeter connects, first, directly to some some lower-current circuits (below the horn relay on the schematic), thence to the bulkhead connector, and from there directly to the alternator output terminal. There's no "external shunt" anywhere in the ammeter circuit. Moreover, note how the ammeter circuit wires are shown as much darker, heavier lines than the other circuits. This is supposed to tell you that the ammeter circuit is a high-current one. If there were a shunt in the engine compartment, the ammeter circuit would be a low-current one that would appear as a thin line like the rest of the low-current circuits.