sitting on fence about amp meter

To maintain the car as original, C130_Chief's suggestion of adding a 10 awg wire run from ALT to BATT+ is best. You can run that either direct to the battery or to the starter relay big post (usually easier).

If you still want a charge/discharge indicator, you can use a cigarette lighter voltmeter. I use one in my modern cars, since their only factory "low battery" indicator simply means "too late". If you want your dash alternator to keep working, but stay protected, put "parallel-reversed" diodes in series with the new wire. See my posts on that, but don't try it if you are an electrical wimp.