Hey I know next to nothing, but heres my 2 cents anyway. If your putting fenders on, use the S-10. You get "modern" suspension, brakes and steering. Plus the ability to buy parts on your way up North (or wherever) at the local autoparts store.
The dude with the '40 Ford cab project looks great (Mud?) but I have to wonder would it have been just as easy (hard) to just build the whole frame? It looks like he put a lot of work into modifying that one. I find this all interesting because I'm getting ready to build a '35 Ford truck and I think (comments please) I'm just gonna build my own frame out of 2x4 steel. It just seems like the best over-all compromise between strength, cost, work involved, and getting the right ride height/stance.