I have a '70 malibu that originally came with a 350 (nothing special). I'm assuming that I have low amp 3 wire alt. now and want to upgrade to a 94 amp 12si 3 wire alt. Can I simply go out and buy the 12si and bolt it on? How do I know if my current setup has an internal or external voltage regulator? I know the 12si is internal, knowing my luck I have the external and will need to rewire half the car. Thanks.