Why 10.7 volt input at ‘71 Duster instrument panel?

The coil should not draw down that voltage. If it does, you have voltage drop AND THAT WILL AFFECT CHARGING VOLTAGE, the old saw, harness voltage drop

The main culprits are the big red ammeter wire through the firewall, the ammeter connections (rare), the igntion switch CONNECTOR, the switch, the dark blue IGN wire going back out the switch CONNECTOR, and of course the connector for the other end, in this case, the cluster/ board. ALSO on the cluster board make certain the pins are not loose, clean and solder if necessary

THIS GETS RIGHT BACK to my usual recommendation---if you have a stock harness with this problem, and don't want to got to a huge amount of work, then break the dark blue "run" wire coming out of the firewall. Use the firewall end to key a Bosch relay, feed the relay with a large wire, say, 14 or 12, fused/ breaker, from the big stud on the starter relay, and connect the engine end of the dark blue to the switched load contacts. THIS WILL USUALLY cure your over-voltage condition as well