Shortbed, not going to haul a lot of weight, but you can still load it with camping gear and an occasional refrigerator. Not many around, nice little truck.
Automatic your Dad was right then, as hoggyrubber says the newer automatics are much better. The trick is to get a locking converter. I'm not sure on the particulars there, just when does the torque converter lockup and how.
3spd there was a transition in the late 60s from the old 3spd (sm318?) to newer Muncie which has a synchro 1st gear. You don't want any ponys in front of the old 3spd. I got very good at changing the slider gear (2nd&3rd) in an old 3spd behind a 300 hp 327. Both transmissions had over drives, but I believe the later with OD is harder to find. The synchro 3spd was available in passenger cars in 64(?).
Rear axle I don't see any way not to change the rear axle ratio, even with an OD. An OD might be a reason not to change the rear axle, your mpg would take a hit. What rear axle ratio depends on engine, 3.08 to 3.55
Engine, trucks don't have much weight over the rear axle, and a short bed has less. Bigger tires are not the answer to good mpg, there is a limit where they will hurt mpg due to weight. There is not much difference in weight between a 6 and 8 cyl, the 6 is heaver. I'd go with a 250 or 283, not the 292 or bigger v8. I would build to 250 to about 220-250 hp. That would be enough cam for a mild lope, for the stop signs.
The proverbial 2s
Larry
