I'm trying to determine which alternator is correct for my 71 Duster, 6 cyl, auto, w/air. The period literature that I have states that there were 3 different alternators used: #3438171 30 amps, #3438172 37 amps, and #3438173 46 amps (heavy duty or spec). Does anyone know what alternator is factory correct for my car, or what the suitable substitutes would be? Thanks.

What is it that you are trying to do? Are you prepping a show car on which points will be deducted if the wrong alternator is found? Or are you trying to repair your car so that the charging system works correctly?

_________________
一期一会
Too many people who were born on third base actually believe they've hit a triple.

I am restoring the car back to factory original. I currently have the opportunity to purchase a NOS 1970 dated 37 amp alternator. It is very expensive, so I want to be sure it is correct for my application.

When I say 'my application', I am referring to the electrical requirements of the vehicle. Do I need a 37 amp alternator, or does the air conditioning require a heavier duty alternator (46 amp)? If I can use a 37 amp alternator, then I have a chance to get a NOS 1970 unit, which would be aesthetically correct as well as functionally correct.

Not sure how expensive it is, but you might want to look into having yours restored and rebuilt to higher amp specs, or get one from these guys:

http://www.qualitypowerauto.com

The only way to know which type of alternator your car originally had would be to look at the original build sheet or window sticker. Usually, factory A/C cars got higher-output alternators; a 46A unit is likely. If you're doing the type of restoration wherein you are happy to spend big money for an alternator with correct date and part number stampings, make sure you're getting the right one; check your car's build date and make sure the alternator you buy could actually have gone on it originally.

_________________
一期一会
Too many people who were born on third base actually believe they've hit a triple.