A '65 300L needs the largest diameter 14" (70 or 75 series) tire you can find. If you could find some 225/75/14s I think they would be great (I need some for my '61 Starfire). What was stock 9.00x14?

225/70/14s, while not ideal on a 5.5" wide wheel, will work fine! My brother's GTX has 10K+ miles on this set of Goodyears.
225/70/14s on 14x5.5" (front) & 225/70/14 on 14x6.0" (rear) Spyder Wheels.

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