Thanks for the reply, Don. Requests on this board don't usually go unanswered so long. I apologize that I said two different sizes in my original post-<span style="font-weight: bold">G77-14 is the size, not F77</span>. I definitely saw "G77-14" on the tires of that GTO and here's a link to the '68 sales manual reprinted on the 1st gen Firebird board:
http://firstgenfirebird.org/firebird...anual/P-3.html
"Wheels and Tires - All Series. 14-inch safety rim wheels are continued on all Pontiac series for 1968. The Catalina, Executive Safari and Bonneville 3-Seat station wagons are now equipped with higher-rated, 8.85 x 14 tires. Catalina 2-Door and 4-Door Sedans have 8.25 x 14 tires as standard. All other Catalina, Executive, Bonneville and Grand Prix models carry 8.55 x 14.
Firebird Series Tires: Firebird - E:70 x 14 Wide-oval Blackwalls; Firebird 400 - F:70 x 14 Wide-oval Redline.
Tempest Series Tires: with OHC 6 engines - 7.75 x 14; with V-8 engines - 8.25 x 14, <span style="font-weight: bold">GTO is equipped with G:77 x 14 Redline tires.</span>"
Feb '68 Motor Trend article also references car tested with stock G77-14 tires.
I look forward to you checking your stock and hopefully finding an elusive "G77-14" OEM '68 tire.