Actually the F-1 engine bay is pretty large since people regularly install the FE big block 460 V-8 engines. The 7.3L Powerstroke is about the same size as the FE engine so it should fit pretty easily. The Cummins 6BT is pretty long and would be more difficult to fit. You would probably have to modify the radiator support bracket.
The 7.3L diesel is pretty heavy at 938 pounds dry; but only about 125-150 pounds heavier than the FE big block. You will have to box the frame in the engine compartment.
What front suspension are you planning on using?
I'm in the process of collecting the parts to do a 7.3L diesel install in my '48 using an Industrial Chassis Dodge Dakota IFS.
Other diesel choices would be an older Mercedes 5-cylinder turbo diesel from the late 1980's. | 
