I bought a 12SI alternator from these guys. It works very well in the new harness and is internally regulated. It is beefier than the original alternator and provides better performance over a "one-wire" racing alternator for street use. It costs about $170. It outputs 140 amps. There is a higher output one available. You need to decide how many amps you need. Do you have electric fans or a high amp sound system? If not, the 140 amp model is fine.