There is no requirement that you have to put a frame from a worn out junk S10 under one of these trucks even though the guys down at the spit and whittle club think that is the only way to do it.
If you like the long bed I'd either sell that S 10 frame and pick up an extended cab frame although the extended cab wheelbase is 122.9 so you still have to find 2-1/2 inches in wheelbase with it. Still maybe someone on here within a couple hour drive has and extended cab donor and wants to run the short bed box and fenders on his AD and is more than willing to swap.
Or just bag he S-10 Idea sell the frame and go another direction on the front suspension. Plenty of MII kits or a Jag XJ front end is stout and the perfect width.
This is on Brandon Thompson's truck here on the board. The great thing about Jag is there is no sheet metal cutting or trimming any place. The steering might be a challenge with some exhaust setups but other than that it is pretty slick.
This is on someone's GMC frame that I snagged for my inspiration file
This is my Jag crossmember when I was doing a wms to wms comparison with an AD axle.
That's just one idea that might work.