Personally, I would repair the existing suspension and steering systems before trying to re-engineer the truck.
I'm certainly not an expert on the handling characteristics of the AD series truck. I am, however, extremely familiar with the handling characteristics of antique vehicles in general. Unlike most people that own antique vehicles for weekend cruises or tooling around the neighborhood once a month, and who drive modern vehicles for the majority of the time on the road, I have never owned a modern vehicle.
All of the vehicles in my signature line are used as daily transportation, rush hour interstate travel, and vacation trips of over 1000miles (the 1995 F-150 is actually my mom's - I just maintain it.)
I will categorically state that the handling characteristics of vehicles of the era we're discussing are not anywhere close to being as bad as many people assume. The big cars of the '50s are not lumbering dinosaurs that wallow in turns and curves or have loose steering or anything like what is often described by those who have never driven them.
When properly repaired/restored and driven within their respective limits, these vehicles, including your AD 3/4 ton truck will perform extremely well and without scaring the daylights out of you every time you hit a pothole or sharp curve.
With modern shocks and radial tires, the performance is even better.
