Alternator wiring 66 Dodge Dart

It originally was an isolated field alternator.
Is it now?
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Verify with an ohmeter. (see Identifying Chrysler Alternators (1960-1976) if you havent yet.)
You may need a brush with terminal and insulator to convert it back to an isolated field if its not and that's what you really want.

Can I ask you then would I be able to disconnect the wires off the welded Junction and just add them to my new 10 gauge wire I was planning to add through the firewall with a ring connector and then continuing the 10 gauge wire to the starter relay
What are you trying to accomplish?
If you want to run a parallel wire to the alternator output wire (R6), yes it can be attached to the ammeter's stud with a ring terminal. Be sure to have excellent crimps and well insulated and routed. If running parallel, 12 gage is plenty and will be easier to work with. If running as a new R6, then 10 ga SAE or 10 AWG (better) will be a good idea assuming factory loads.

I don't see why you would need to a 10 ga wire to the starter relay bypassing the ammeter and fusible link. The battery doesn't run the car. It just for starting and when the alternator can't supply power. The ammeter shows how much its charging or discharging. If its discharging while the engine is running, then there is something wrong withthe alternator or alternator circuit.