Definitely sounds like the alternator belt...was your radio turning on and off just before it started dying on you? Check the other belts, the tensioner for the alternator, and your harmonic balancer/crank pulley to make sure its ok. I dont know about the 420a but the 4g63 pulley likes to come apart.

About the portfueler...what turbo/how much boost are you running? Stock injectors and ECU? If you're running more than 5psi on the stock injectors and ecu, I would definitely stay out of boost till you can get the extra fuel.