I was looking at Barry's site and there's a lot of confusing information. Initially:

- M73 front/rear for the R/T
- Then, in Sept 1970, M71 front-only introduced for the R/T
- Additionally, in Sept, the rubber bumpers became available for base Challengers but the code for them were A21 and A22.

At least that's what it seems, as strange as it sounds.