There are several approaches to this

It depends on how non-original you are willing to modify the car

It depends on whether you insist on an ammeter

It depends on added accessories, and the load on the sysem.

Just upgrading the wiresize and eliminating the bulkhead connectors is a huge first step.

Keep in mind that the ammeter itself can heat up and fail. "at least some" models I've seen use the plastic mounting of the dash to actually hold the ammeter together and make the elctrical connections. This means that any heat or looseness causes MORE heat and then catastrophic failure of the ammmeter connections, melted wire ends, etc.

If you are in love with ammeters (I am) the BEST approach, and there's been discussion of this--is to figure a way to convert the old "full current" meter to one like used in the later '70's. These meters were a sensitive milliameter which used part of the car wiring for a SHUNT (external shunt) and so the only HEAVY wire coming through the bulkead was the supply conductor to the interior of the car.

All the heavy charging/ ammeter circuits remained under the hood, the ammeter conductors being small no18 or so wire.

I BELIEVE I found a site of someone doing a few of these meter conversions. I'm sure it would depend on the ammeter---the smaller round ralley gauge used in the RR/ Chargers could be a beaouch