alternator output

You should bypass the dash ammeter. Search for "MAD Bypass", gazillion posts here. The stud connectors can melt even w/ normal 30A output, so 80A would stress them. Any corrosion and heat builds up. Even worse, the bulkhead connections can melt under full alternator current (exc. 1963 & 65 cars w/ buss feed-thrus). 13.9V when running is "about right" for the voltage regulator set-point. I see ~14.3 V in my newer cars. 12.6 V is correct for a fully-charge battery w/ engine off. Some replace the dash ammeter w/ a voltmeter (modified wiring of course). Until then, use a cigarette lighter voltmeter, as I do in my modern cars which have no built-in gages to monitor charging. $15 for a nice digital one or $5 for a Harbor Freight cheapie w/ LED lights.

I posted a method to keep the ammeter working normally at low currents, then shunt higher output straight to the battery to protect the cabin wiring, using large diodes, but that is beyond most people's abilities to understand and execute.