For a little background, I acquired the Willys a few months back (cheap)and spent alot of time and money trying to get it running with the original four banger, but have given up, I just cant keep it running. btw-the stock drive train gets about 12 mpg, and tops out about 45 mph, downhill with a tailwind.
I realize it will be underpowered, I expect this to be a put-put truck for cruising backroads and 4 wheeling.
When you compare the numbers, it may be a good fit: The HP and torque are about the same in the Willys f134 and the sd22. The weight of the Willys truck and my 82 Datsun are within 100lbs. Alot of people think the old Willys were sturdy, but they were originally spec'd to weigh under 2200 lbs so that could be air transported.
The height, width and length of the sd22 and F134 are very similar, the sd22 is a touch longer but nowhere near as high. The hard part is the Nissan 5 speed-that thing is like 14 feet long!
Here is where I got today, everything is just mocked up:

