Thinking way outside the box Gear Vendors might have a unit that could be adapted to fit the 4 speed in your truck.
https://www.gearvendors.com/f2wdt.html You would have to change to an open driveshaft which would involve some drivetrain re-engineering. A downside of keeping the 4 speed is the lack of syncromeshed gearing. I swapped out the 4 speed in the tonner for a 49 Merc O/D transmission and that swap made a big difference in its driveability and usefulness. Just food for thought.