Stock alternator up to the task? If not, how many Amps will I need?

I ran a 100 amp alternator in my Challenger for like 60k miles, all stock wiring, no issues. Now, the only additional load on that car was halogen headlights and a stereo with a couple of 6x9’s, so no real big amp draws. So, it’s unlikely it ever pushed serious amps through the system.

I also run a 100 amp alternator in my Duster, again with the stock wiring (currently). Mopar 3 wire set up with an external regulator too. That car has a Ford Contour two speed, dual electric fan set up that can pull a whole crap ton of amps on start up (40+) or on the high speed fan setting. It also has a A/F gauge with a wideband o2 sensor, stereo, halogens, etc. It’s held up fine for a couple years now, although I did clean up the bulkhead connector and inspected the amp gauge. I run a continuous duty relay as part of a cut off switch and battery relocation, as well as separate relays for the fans. But it still has the stock amp gauge and wiring so at some point that draw goes through the ammeter and wiring.

Now, I would not say that’s the ideal set up, not at all. And I do have plans to convert both cars with an amp gauge bypass and voltmeter. But it’s been awhile and nothing has melted or burst into flames, and I do keep an eye on the bulkhead connector for signs of trouble. The bypass definitely is the better way to go for longevity and safety, but the factory wiring can handle more than a 65 amp alternator if it’s in good condition. And yes, that’s a big “if”. I was fortunate and both cars have stock wiring that’s in good condition, not hacked to death stuff like a lot of these cars have.