Would an alternator dated September of 69 with a 69 stamped in the starburst be correct for a 70 challenger.
Thanks,
Mike.

Depends on the SPD of the Challenger but typically, yes.

When was the car built? They started production of the 70 models around July, or August of 69, so a September alt would't be right. Look at the scheduled build date of the car. Some of the other guys on here can refine this better for you.

Thanks. Don't have the build sheet. But its hard to find one, especially one with the dual pulley for a/c that I need and for $150. seems like a good price.

Fender tag date?

unfortunately I lost that 25 yrs ago when it was falling off so I took it off when I had the engine compartment painted. It kills e that I lost it.

Moot point to worry about date codes then

If the door sticker is still there it will have the month the car left the factory

Mike - Most a/c equipped 1970 e-bodies left the factory ith a 3438178 numbered alternator. If you have pictures you should also see the pulley numbers "711" as the last three digits stamped into the pulley hub face. IMHO for $150 asking price, the alternator core needs to have all its original hardware and a non rusted pulley.

Also, if you think you have the original K-frame in there, that date code is supposed to be very close the the completed build date of the car. It is on the front vertical surface centered usually , and has the 3 digit day followed by single year digit followed by shift. That should get you a very close indidcation of final build date.