The NAMC’s “Catalog of all Series Matchbox Models” (second edition) states that the c/a version (Nick's variation code 1) only occurs with dark GPW, whereas the 7.5 x 18 GPW r/a variant (Nick's variation code 2) can come with either light or dark GPW. The 8 x 18 GPW r/a model (Nick's variation code 3) is listed as only coming with light GPW, but both the AIM's “1-75 Series Regular Wheels” catalogue (second printing, 1983) and Houghton list this model with either light or dark GPW.
U.K. Matchbox examined the model in Vol. 6 no. 6 (Feb. '83) p209, with a follow-up (discussing boxes) in Vol. 7 no. 1 (Apr. '83) p23. The article states that early models were hand-trimmed before assembly, and later models were mask sprayed after assembly, the difference being easy to spot because the former have a black baseplate tongue in the bumper slot whilst the latter have a silver-painted tongue. It therefore seems likely that at least one of Nick's variation codes can be found with either style of trim. Information please!