Realizing these are NOS (dated 1975) and not assembly line this is how I think they should look. PIC was saved from an eBay listing years ago. I have a set of NOS TA/AAR mufflers with the same 1975 date that look identical. As far as I know another run of NOS muffles in 1979 did not have the black paint and had a smaller penatstar.

Probably more detail than you wanted though...