How fast to you want to go and are you prepared to make additional improvements to your truck.
Remember they didn't have freeways back then, so most of the old trucks were designed for milder speeds say 35 to 45 MPH. Freeways were just coming into play in the mid to late 50's.
That is not only gear ratios, but also stopping power, i.e. BRAKES, wheels and tires. Front axle bearings, sway bars, wheel alinement camber, etc. etc.
