Hey Dyno --- what is the wheel/tire size on the 3/4 ton you are looking at. The 4000 series (1.5T) and up all have the 20" wheels while from there down they range from 15-18" and make a big difference in the appearance as well as final drive ratios (on the rear). The smaller wheels are fine for a "rod" look but really alter the overall appearance quite a bit. And, like I said...small tires make a huge difference in top speed at "normal" rpm. I've heard there are a few modern 19.5 & 20.5 wheels that can be adapted though. They would be close to the original look, allow for much better radial tires and, keep the drive ratio up near what can run at anything near highway speeds.
Good luck, looks like a great project, and as I noted in a couple of your other posts, I would be very interested in the ring & pinion you take out if they are 5.43:1.