ammeter

All wrong advice for a 1965 (or 1963). They have dedicated "buss bars" that feed the big BATT and ALT wires thru the bulkhead (look at yours). You don't need to do anything other than clean those bolted connections (sand to shiny, coat w/ di-electric grease) on the engine side. On the cabin side they are soldered/crimped, so no problem. I put a 65 bulkhead in my 64 for this reason.

Other places to check are good clean connections at the ammeter (rear of dash) and that your under-dash "ALT" and "ACC" "fused junctions" aren't corroded. You can find photos of the later (under wrapped tape. My junctions were a bit green in CA, so an MS car might be worse.

The V-8 shouldn't matter, as long as you didn't upgrade to a non-factory >100 A alternator (modern Denso or such). For that, you could install a "diode bypass" that I designed, but only for hard-core electrically smart guys (engineers or techs).