It sounds like a BB with AC? If the old small case MOPAR style isn't enough - and it sounds like it isn't - its tougher to upgrade with AC. The pivot and bracket bracing is different than non AC cars.

With stock style heads, you may fit the GM case Powermaster 140 A unit. I have Ed heads and not enough clearance. I bought one and had to return it. I ran the 75 A Powermaster MOPAR alternator for a while but it wasn't enough. Discharge at idle and barely enough when running with brights and AC.

I wound up going back to the "big case" MOAPAR alternator and brackets from my core engine ('78 Cordoba). Its 100A with lots of idle output. Its a little heavy but performance is great. Rebuilt 100 A alternators are available on order from the chain part stores

I had to extend the water neck about 1 1/2" so the radiator hose would clear the belts and mount the receiver/dryer about 1 1/2" back (Challenger) to clear the alternator since it sticks out more.

Pic in the attached document.