Obviously, we need someone to have an actual Pontiac bulletin showing the mid-year addition of Goodyear Polyglas white letters on the 68 Firebirds. I'm assuming that the author of that link provided earlier has proof.
If the Goodyears were available mid-year on the 68's, it wasn't in the original sales album, or the ordering form, that the dealers had. Therefore it must have been a Pontiac bulletin announcing the availability of the Goodyears.
As a sidenote, the link provided doesn't say anything about "white letter" Goodyear Polyglas, just "Goodyear Polyglas". The Goodyear Polyglas tires were produced in a 3/8" inch white line stripe. The Goodyear Polyglas GT was the white letter version.
I believe I have seen white stripe tires on 68 Firebirds in an old original road test, but I have never seen the white letter Polyglas GT's on a 68.
