Jim, remember though that the Goodyear RWL was indeed available on the 69 Trans Am. But of course this option would not have appeared in the original 1969 Firebird sales literature because the Trans Am was a mid-year offering.
The "G's" were definately NOT an offering to my knowledge.
If Pontiac made something available mid-year, they would have sent bulletins to their dealers, and if necessary, provide an updated ordering form showing the new option(s). The 69 Trans Am bulletin listed the new Goodyear RWL tires as an available option, and far as I know, this was the first use of white letters on the Firebird.
Never say never on the RWL on 68's, but I would like to see documentation.