How would this Alt. perform with underdrive pulleys?

A common misconception. Many of the really high output units in car audio competition put out only a few amps at idle.

For A/C & a little audio? a brand new 70 to 80 amp unit if you want to stay stock appearing. You will lose a little idle output with the underdrive pulleys.

Or a 3G/4G hybrid with a stock stator. The 3G puts out around 70 amps at idle, with a top end of 130 stock. This would be an internally regulated unit.

We discussed these two units last year:

http://www.forabodiesonly.com/mopar/showthread.php?t=166513&highlight=cargo+alternator

I have not bought another mopar style alt since then, but do give John a call and ask him what he can do for your car & budget.

B.