Mine runs between 13 and 14 volts, depending on the draw of the system. Some of those 130 amp alts have an external regulator, while all of the ones Ive seen on the 6ers are internal. that would account for the different plugs. There will be a difference in cost, so make sure they give you the right one.

Sounds to me like your problem is the regulator, not the actual alternator. Im not sure how to service the internal regulators, but you may be able to just replace that, they bolt on the back. If you replace the alternator, opt for a new one, otherwise you will end up replacing it 6 times and causing more electrical damage, including the battery and starter, at least thats been my experience.