Round back to square back alt

So embarrassing. VR was not grounded very well against firewall so I ran a wire from the casing to the Neg. battery post and things settled down a lot but not completely. Ammeter still not stable enough and would occasionally stay left of center on gauge for a minute then flick back to C side. I ended up returning the round back 60 amp alternator for a remanufactured square back 45 amp unit. Returned the mechanical VR and replaced with '70+ electronic VR. So Dart is now using both field terminals on alt and everything seems right. Steady gage, bright lights always, no flickering. A big improvement.
My electrician looked at the 12V wire to the alternator and was shocked how small the factory wire is. He said that size wire is good for 20 amps max. So I Googled it and AWG (American Wire Gauge) ratings and charts show a 60 amp current should use a #6 gauge wire. That is a 1/4" diameter of twisted copper strands under the insulation. So how are these small wires holding up?
Here are the parts I used:
NAPA Premium+ 2132009 alternator rated 45-50 amps
NAPA Proformer VR38SB voltage regulator
Charge!