I would say you don't want to run the alt power through the ammeter.
The meter in you rated is rated at what 15 A or 25 A.
Even if you only have a 65 Amp alt, you are risking a burn out.
When changing to an alternator you should wire direct and convert to a volt meter to monitor system condition (or leave the ammeter and run a power wire from the fuse box to it to keep the rest of the wiring the same).
Running that much current through the dashboard is not a good idea.
