What is the bias ply tire size for 1963 Grand Prix?
I don't even believe bias plys are available anymore. I had a '77 Cadillac that had them, 28 years old at the time, still on with 30k original miles. IIRC they had similar size ratings to radial tires.
Search Pontiac Grand Prix Questions
Are you a UK consumer? CarGurus now has a discussion forum in the UK.
Pontiac Grand Prix Experts