Yes they will fit on your D44. not sure on any width differances you might see a little increase. Although I do beleive they use the same lenght outer axle shafts so there may be no increase. Of course you will need to run 8 lug wheels to use the F250 knuckles. I believe you can use gm 3/4ton knuckles and run 5 on 5.5 wheels
High steer is really the only advantage to running flat top knuckles so if you have a tall lift and steering issues then that may be the answer. Otherwise I dont think they are worth the effort