If you look here on page 20-21 in the Fatman catalog, you'll see they call it the, "Extreme IFS," it's based on the 70's/80's GM truck suspension.
Fatman.I'll agree with what some others have stated. It may be worthwhile to get the truck running and driving before jumping into things. I didn't see what series you have, but it may be possible to swap components from other trucks get the ride and look you're after. The 4100 trucks share much of the same architecture with the 3800's, So swapping out front leaf spring packs, and or other suspension components may be possible. On the rear, you may be able to just take a few leaves out to get what you want.
The "Big Bolts" have wider front sheet metal than the 3100-3800 trucks. So, swapping out a complete chassis with a late model one is always a possibility. You see this done with early cab-over trucks and wreckers all the time.
Anyhow, it's you're truck, your decision. I hope we helped.
Chris
