Thanks for the Tremec calculator information. Encouraging they and I were at the same place...nice to see, actually.
What I've learned about these is that shallow rubber band type tires are not good. The thinner the tire, the worse it all works and the less you'll enjoy driving it. And the less wide the tire is the better, also. Wide tires tend to not steer very well on these trucks. The suspension in them wasn't made for comfort and the steering works best if all things are like new (kingpins, kingpin bushings, bearings, tie rod ends, drag link ends, all balls, etc...by that I mean no steering play) and if the tires are as close to the original as possible (in terms of diameter and width). Why? Because some things like camber are not adjustable. Well, they are but you won't find many shops today who can do that without screwing it up badly because the axle has to be bent in a cold state (NOT HOT) and once bent it will be out of adjustment for any other tire/wheel except that particular one. There are two adjustments: toe-in/toe-out and caster. 600 x 16 inch tires were used back then and they were crazy common...used on scads of vehicles and may have been the most common size. Now they're essentially gone except for some high dollar repro tires. I use 6 lug 15 inch wheels and P205/75R 15...Hankook Optimo tires I bought on Amazon for something like $55 each a few years ago. Maker claims a diameter of 27.1" but it seems more like 26.5" to me. I expected a pretty horrible tire for that price but they're quiet, have great grip, are all-season, stay balanced and wear very slowly. As I said, thinner tires will steer better and will perform at higher speeds just fine. Plus this size will take bumps really well. A thin tire on an 18" wheel will let you feel even the small bumps. Just something to keep in mind...
Here is an article on low-profile tires which mentions pickups:
https://carbuzz.com/features/what-are-low-profile-tires-understanding-the-pros-and-cons/
