I also have a 1940 3/4 ton. Why change just the rear end? If you are changing the rear for an open driveline, it stands to reason you would upgrade transmissions at the same time... say to a t5.
So I'll make a list of questions...
What rear end are you going to use?
1940 3/4 ton has a 6 on 5.5 lug pattern. 1947 3/4 ton is an 8 lugger.
What are you trying to accomplish?
Better gears, better braking, more transmission options? Are you trying to use parts you have? I am confused.
What engine will you be running?
