that doesn't matter to the alternator, if the amp meter worked before, it will still work.
Personally, I'd remove the amp meter, wire the alternator direct to the battery cable at the starter with only a largish fusible link, then replace the amp meter with a voltmeter. But it will work fine with the original wiring.
I think in a lot of cases, the generators were not powerful enough to raise the voltage that much, and so an amp meter was needed to indicate charge or discharge from the battery. amp meters/ammeters were probably cheaper to make than voltmeters. The problem was you had to understand how charged the battery was for the amp meter to mean anything. An alternator usually either works or not, so it puts the voltage up to 14 even at idle, or it stays 12 and drops fast, so a $2 voltmeter will tell you the alternator is working.