I agree with 6bbl. 60-series 14" tires are short.
FWIW, decades ago I had a '73 Dart, Slant/Tflite, that I used to commute, which included some 65-70 mph time.
I wound up with 215 & 235/70s on 15x7 steelies, which were a tight fit; rears could rub with backseat passengers.
Helped with the RPM/MPH a lot, not so much acceleration, but it was slow even with its stock 14s.