I have Dakota Ubolts on my 8.25 diff in my Dart.
They have the flat area.
The diff I have is an original 73-74 Mopar 8.25 with Jeep Grand Cherokee gears and sure grip in it with the Cherokee disc brakes.
The Mopar 8.25 and the Dakota 8.25 both have 3 inch tubes, as does a 8.75.