anyone know stock '68 alternator amp output

First your alternator output. As far as I know, no remafgr' has ever sorted through the different parts. So if you have a remfged alternator it can be any one of the 3 different output ratings ( 36 and 42 the most common ).
Now about wiring harness concerns... Resistance in circuitry causes heat. In many cases that's by design. Your thermal gauges are a good example. A mere 3 volts pulsing through this circuit generates heat in 3 resistor coils to move 3 gauge needles.
Same resistance happens at weak connections and in some cases the location of that is also by design.
To bypass the old weak connection at the fusible link and bulkhead connector outside in the engine bay will simply move that weak link to other locations inside the cabin.
Sure some amp gauges have failed but no more frequent than ignition switch connections, headlight switch connections, on and on. I do have issue with the amp gauge, how they are wired into a system. Its failure will shut down the whole car. So I wont argue with replace it with a volts gauge ( madelectrical pages wont help with that ).
Nobody will periodically service and maintain a wiring harness. Service and repair as required is the norm.
I just never will see the madelectrical method ( drill through and shove continuous wire though the bulkhead ) a proper service repair. New wire terminals are available. Previously unused ports in the bulkhead connectors are present. Thus a proper service repair is doable.