12 SI Alternator, 78 or 100 Amp?

I'm using two no 10s. I'd use that or 8

I guess you realize that originally, all charging current went INTO the interior, through the ammeter, back OUT the interior, and to the battery, along with interior car loads, ignition, headlights, etc

By properly rewiring the car without the ammeter, you eliminate the charging current "going in" so in a sense you relieve some of that strain. But adding modern electronics, etc, you still want plenty of capacity