thanks Kurt,
looking at '68 CBC's it appears the trim block actually refers to the color of the hard metal interior items, i.e., dash face, top of doors, outer edges of the rear package tray, etc...
however, I've come across a couple '69 CBC's one with an "M" for a 713 car and one with a "P" which I think may have been a Ivory/Black or Ivory Houndstooth car, in either case, both use black trim so I'd of thought they'd of used an "A".
unless the Houndstooth interiors used unique codes, so go figure...
thx,
Mel