I'll have to check for these at Carlisle. I can't find anything online and parts manuals say AR (As Required). Mopar parts books are so bad.

Front or rear?

Both.

Pretty sure it's just one of the cylindrical ones in the frt license plate bracket on all 71-4 B bodies.

Thought there may be some differences between Dodge vs Plym for the rear license plate bumpers.

I did just stop by Roseville Moparts today and see (2) 3/16" holes on the bumper under the lp on a 71 Plym. So I'm assuming its 2 of the smaller bumpers like the 1 used in the frt.

The only 2 options for lp bumpers are a cylindrical one about 5/16"dia x 5/16" tall or a larger one thats more the size of a gumdrop with a flat top that fits a 3/8" hole. (These later ones are used on 68-70 Chargers andf Challengers)

71 2dr Satellite/RR/GTX
Front and rear are the same. Original in the photos

Wow. Thanks!