My dad had a 477 in an F-880 Tandem axle grain truck. he could put 30K on it and it would get where you wanted to go, just might take awhile. It had a 10 speed fuller, and it would turn 3K at 55. Didn't matter if you only had 5K lbs on, when you were loaded, even a little bit, you used every gear in that tranny. running down i-75 to the grain elevator and back ~30 mi round trip, using the "georgia overdrive" on the one hill that would maintain 55 MPH, the truck got 2 MPG. It was a good ol truck though. If you could find a crank, I would stick it in there, it would be worth fixing, if you could pay the gas bill.