alternator output

Rebuilt a 318 74 duster, put an 80 amp alternator on it, a new one due to the fact i put ac bracket from a 90 ramcharger ,had to put a different alternator to match bracket, my alternator gauge is pegged to top at 40+,,but with ohm meter i read 13.9 volts at battery when running, was 12.5 before starting car, my question is, do i need to disconnect alternator gauge since it's pegged, and is that normal?,,Also should i replace alternator gauge with volt gauge and splice the red and black together that went to alternator guage?