You don't need a new alternator nor a one-wire alternator. You can use the factory alternator if you can still mount it up. You are correct in that the PCM controls the regulation of the alternator, but it's not that complicated. You can install another external voltage regulator to your existing alternator.
Your voltage regulation is an "A"-type in that the field is controlled on the ground side. The voltage regulator is simply controlling the output of the alternator by switching the field current on-off to a ground in the PCM.
You have two small wires...right? A White and Dark Blue on pin#1, and a Dark Green on pin #2. The White and Dark Blue is battery power with key on. The Dark Green is the switched wire.
Connect the White and Dark blue to Key-on battery source (fused). Attach an old school external voltage regulator (type A) to the Dark Green wire. The 71-up electronic 2-pin VR off any Mopar should work. It'll need to be securely grounded and it will need a voltage sense (battery voltage) wire so it can tell when to charge and when not to.
An old Mopar performance book can give you the simple wiring diagram for the two wires on the VR. The VR is cheap and easy to find at any auto parts store. The triangle shaped plug is easy to find also.
The earlier 70-down electro-mechanical VR's were B-type. They were switched on the power side. Actually either one will work if it's wired in correctly.
Piece-o-cake.
