[John Brown]

Since I'm not at home and don't have my books with me, I'll have do this from memory. Most original 68 cars got the black caps (D308) without the "R" . Black caps had aluminum terminals. In 69 the black caps got the "R" and a new number (D308R). The brown caps (with copper terminals) were used on some T.I. applications and lots of HD trucks, including International and White, that used Delco distributors. The brown cap used the number (D309) thru 1968 . The brown "R" caps (D309R) weren't introduced till 1969, along with the D409R rotor. The combination was to cut down on radio interference, probably had something to do with the up coming "antenna in windshield" fiasco. Either that or Federal regulations like those in Canada that require RFI supression on lawnmowers, not sure which. C.D. ignition on Chevy taxi, Olds and Pontiac used a red coil and a matching red cap.