I found out problem with fitting stereo speaker covers to the dash on my 70 Challenger.
I had five of them and only one fits good, rest does not match the dash surface and sticks out.
The one that fits has J/L marking, other have B/L or B/R

L and R is left and right - that is clear
but what is B and J?

I checked parts catalog, but I have only 70-71 one so have no info about 72-74

there are different grilles for 70 Challenger than for 71 Chall/70-71 Cuda.
In the catalog J is Challenger and B is cuda so it looks like that lettering on covers matches model.
72-74 Challengers probably use the same grilles as 71 Chall and these are marked with Cuda sign

70 Chall had different dash pad than other years - that is probably connected with speaker grilles also

in the catalog there are following numbers:

2884691 right 70-71 Cuda, 71 Chall (probably B/R)
2884687 left 70-71 Cuda, 71 Chall (probably B/L)
2884682 right 70 Chall (probably J/R)
2884678 left 70 Chall (probably J/L)

the ones I have do not match these numbers
B/R 2884685 - 2884690BC
B/L 2884685 - 2884686BC
J/L 2884676 - 2884677BC

they are similar but only J/L matches my dash
I enclose picture that compares both left ones, You can clearly see the difference on the edge

anybody knows more about it?