I am no expert on these but I think they could be. I installed new 3:73 gears from a 3:08 and the speedometer @ 60 mph is actually only 47 mph.
28" 255/65/15 tire on a 7" rim. If I can get a range of gears I should be able to zero in on the correct one.
Probably available at Napa and rockauto, same as a powerglide, Saginaw, Muncie, t350, as far as I know. There is a calculator on line maybe where you can enter your tire size, etc
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63 Parisienne sport coupe (The Big GTO), black, maroon interior, 409 4 speed; former owner of a 59 El Camino, 63 Corvette SWC, 62 Chev Bel Air SC. 1963- Pontiac top selling car in Canada
Mahone Bay, NS Still not old enough to need an automatic