Another option would be to change your
ring & pinion gears to a 3.38 ratio. This is not cheap but it accomplishes what you want.
My '54s have 3.90 rear ends and I find that I can cruise at 65 mph because my tires (truck radials) are about 3.5" wider diameter than stock tires. My brakes parts are all new and all front-end parts are in good shape, so I do not worry about the higher speeds.
