Why 10.7 volt input at ‘71 Duster instrument panel?

I’m re-reading this thread this morning and I discovered the link you provided to the MAD catalogue. Wow - what a great “electrical systems for dummies” that I need to fully review. Thanks!
Bear in mind not everyone cares for how the bypass is done there, if you decide that. Most of us have come to the conclusion that you either eliminate or repair the terminals through the bulkead, then add a large fused/ breaker protected wire direct from alternator to battery, leaving the original in place. Then use a voltmeter

There's an old thread on here on building a voltmeter into the old ammeter cavity

It may be that the voltmeter suggested for use in here is no longer available

https://www.forabodiesonly.com/mopar/threads/ammeter-to-voltmeter-who-does-it.119480/