BigHog, "I really want to be able to run with modern vehicles on the road". Ultimately this means front to rear drivetrain changeout. Let me see if I can draw a mental picture.
1) AD trucks:
Stiff leaf springs, straight axle, flexible frame and the cab on pads (with humans inside) that move or sway with it. This is the way GM designed it to work. Not designed for high speeds in a curve or a quick-agile (thread-the-needle) lane change, on a crowded expressway, at 80 mph. On a modern expressway near a city you have to concentrate harder and think-ahead. It's tiring. I try to avoid congested areas by taking the backroads.
2) Modern trucks/cars:
Stiff frame. The front and rear suspensions takes, or tries to take, all of the movement away from the humans inside and negotiates everyday modern traffic.
To make 1) into 2) requires $$,$$$ unless you are good at safely fabricating parts/material into what you desire. Add to that the time and shop equipment. Maybe it would help if you first determine the amount you are willing to spend on your project then work backwards to see what you can afford to do.
I wish I had the video of a stock Model A "50's hotrod", modified with a "hopped-up" flat head V8, trying to take a sharp turn in a vacant parking lot. They did it, but with only two wheels on the road.
