Trailblazer chassis with the I6 or swap in an LSx.
I wouldn't waste any time trying to swap a Vortec into a stock chassis on this truck. The antiquated I beam front and more than likely low ratio rear end will take the fun out of a V8 swap. These trucks were built for farm use, not heavy travel. I work on a '49 Ford F2 for a guy that is pretty much stock. It is a blast to drive around town, but tops out at 50-55 mph on the highway due to the 4.86 rear gears. He has mentioned swapping out the I6 to a V8, but that would ruin the truck IMHO. It is just a nice old original truck that turns heads everywhere you go in it.
As for this international, there is very little restoration parts and service parts available for it due to its rarity. If the cab & bed are nice, then I would seriously consider a late model chassis for it. The trailblazer deal is closer in size to these old trucks. At that point the title doesn't really matter, but I would definitely get a bill of sale for future paperwork.