I have a 58 2-ton with a 327 in it. 9r22/5 tires, The engine spins 3600 @ 60mph and 4200 @ 70mph. Umless you find one with a 5 speed Overdrive, or change out the rear end for something with more freeway gears, you will be spinning the same RPM. A lot of the 5-speeds were not overdrive trannys, I believe most were direct drive on 5th.
It will also still have manual adjusting brakes.
The 6400 is the shorter truck with 13' bed, the 6500 was longer, I am not sure when they started making the longer ones though. I have seen a 1956 6500.
