[POWERSTROKE]

If you consider how some of these old pickups were used they really needed those 4. or 5. something axle ratios, and the relatively low top speeds to make the 120+/- 305's work that hard.
In a 3/4 or 1 ton a 351 would be a better engine choice, I had mid-1960 GMC pickup sales brochures decades ago, I'm not sure there was a larger engine option.
Today it's crazy the performance you can get in a pickup, like my 2018 Ram 1500, 5.7L 345 cid V-8, 395 hp, 410#/ft torque, 3.92 axle ratio runs 80 mph at 2000 rpm. And it tows like it says KENWORTH on the grill.