According to Sheldon's site, the use of the W came about after '74. A 1973 frame may have used said G, without the W, but it would then be followed by a four digit number rather than six. Subscribing to the WG scenario would put this bike at a 1983, which I think it predates. Plus no stamped 'r's anywhere. The track bikes had the bb's cut in the mid 70's as well, I believe.