Building a tow rig or a truck that will haul "who the heck knows" means that the s-10 chassis front end will be too light so immediately your left with swapping in and using something heavier. That would account for the FWD motor home chassis or perhaps getting an Eldorado chassis or similar. Personally I would build my own frame and decide what I needed for the job as to the suspension(s) and running gear.
Might as well make a complete custom as to start chopping something old up if you want a modern cruiser.
2"x5" tubing works well and crossmembers can be salvaged from a wrecking yard. Truck frames are a fairly simple and straightforward design.
