I wanted to do this to my 97 250. I got a dually rear frame clip with 6 wheels from a 96 350 and the frame is about 3" narrower than my frame now, I could cut the spring perches and move each one 1"5/8 out then use a 1/2" spacer to push the wheels out away from the springs then I ran into the problem of the springs, they are 2"1/4 wide and about 4" shorter eyelet to eyelet, the bolt pattern for the shackles are identical but you could only use the factory shackle location for the front or rear in order to keep the rear running true and straight, then to compound the situation further a new driveshaft would have to be made because the length would be shorter or longer depending on which shakle location you chose. With the right resources and or money this would be very doable. I bought the whole swap 6 wheels w/good used tires , and rear clip for $200 front dually hubs were also included