You probably have an F-150 truck rear end. 3 1/4 tubes. The ends should be the large bearings...good. The very end should neck down to 3"...still a problem. You will have to get a hold of Mosier for exact details. They have a flange end drawing on their web site. Moser Engineering.
I have one in my 41 Willys and have gone throught he problems. Parts all fit....almost. you will have to make these small adjustments . Space between the flange and axel, 5 inch bolt pattern, (have it redrilled if you can't do it yourself. if you go to rear disc brakes the normal brackets don't quite fit....rework them.
The bottom line is measure everything twice and cut once.

bentwings