Two things: 1) will the 70 amp model even have the same bolt pattern as the 80 amp model that your car is designed for? 2) How many amp does your car draw under heavy loads? How many amps do you need if you're using the A/C, with the strereo on, with the headlights on? Since you can get a remanufactured alternator for less than $100, just use the right one. Or even cheaper, you can buy a rebuild kit for less than $50. Most of the time the alternator's bushings or some other simply-replaced internal part fails. So with this in mind, a rebuild kit is the cheapest way to go, providing that you're so mechanically inclined.