What's your top speed now? What do you want your top speed to be in a 77 year old truck?
I drive a 1950 3100, 216 3spd with 4.11:1 rear end. It has stock 16" wheels with correct sized tires. It tops out at 65 but I drive it 55 - 60mph a couple hundred miles every week. That seems fine to me for a 73 year old truck.