Running a heavy wire from the alternator output post to the battery or starter relay of there is one will bypass the ammeter and support running a 100 A alternator. One 6 guage wire should be more than enough. Its recommended to splice several inches of fusible link in the 6 guage wire to protect the system from serious shorts. 10 guage fusible link should be about right and is available at auto electrical stores. The ammeter wouldn't work with this change. An accessory voltmeter would be a good replacement.

Another and potentially bigger issue is why the car "cuts out" with high electrical load from the AC. Even with a small alternator it should run OK for quite a while on battery power. OE Mopar's were orignally designed this way; they would discharge at a stoplight and "catch up" running down the road. It sounds like the AC may be on a weak or overloaded connection on the original donar car's wiring. Original AC would draw +/-15 amps so if you're pulling 35 that's too much for the original wiring. I'd check all connections and consider running a dedicated power supply for the AC with 10 guage minimum wire from the starter relay or battery with an appropriate fuse. 35A sounds like a lot for AC but I guess the manufacturer knows

The 2 field upgrade will help and may be necessary depending on what alternator you choose. Consult a wiring diagram for a 70 or later Mopar as a guide. (I don't have access to one now).

Good luck.