Drivers side mirror parts question

[veeprov35]

Part numbers question. I am working on locating the driver side mirror. It is the two post manual. I have come across two part numbers that look like what I need. 2299574 vs. 2299521. What is the difference between the two and will the 521 work on the 66 Dart? I think the spacing between holes may be the same. Also how can I tell if it is OE or aftermarket? Would the part number be missing? Any info would be greatly appreciated. Thanks.
Also is there a parts numbers list somewhere. I could only find a book that was $300 - yikes!

 

[Rick@Laysons]

The "521" piece has a thicker edge around the perimeter compared to the "574" piece.

Typically, the "521" are used in the earlier years and the "574" for the later early A-body years.

For a '66 Dart, you'd probably want the "574" style. The "521" would fit and function, but the "574" is more likely correct.

 

[Bogie]

My Mopar has both Service & Parts books online.

My Mopar