Actually I did read your post correctly , you might be able to stretch the housing if you chain the housing to a light post & hook a cummins to the other end you should be able to pull the light post down on the Cummins truck !! Don't use the light post in front of your house so you don't get caught !!
If you want a slightly narrower housing you might get away without new tubes you could compensate with different offset wheels or move the springs in as well , , I wanted a stock diff replacement & the tubes came up too short , we had to swap in new tubes . My friend & i have built 30 + danas from ford diffs from the wreckers but this was the first stock width one we had built & it was just to short once the ends were trimmed off , I also did a diff for my 71 Charger & it is slightly wider than the Chall diff . My diff for the chall turned into a nightmare , we used the ford taper roller brgs for the first time so I special ordered the ends & brgs , then ordered the axles from Strange , we were told Strange didn't have the ford ends or brgs , after ordering the axles found out we could order the ends & brgs installed & could have saved a bunch of $$ that way , the pinion seal failed as soon as it was installed , the yolk pinched the spring !! I powder caoted the housing & they cahrged double what I was quoted , the diff should have come in under $1000 & cost close to 1800 said & done , I should have just ordered one from Dr Diff !!
The backing plates are just std Mopar ones , the housing ends use the Mopar 5 bolt flange with the Ford Brg so I used normal Mopar 5 bolt backing plates & 10 " drums , they use the same backing plates on all Moper diffs , the 8 1/4 uses a 4 bolt end flange but still uses the 5 bolt backing plates