There are differences .....the RSC equipped vans have ABS sensors on each rear wheel (needed for RSC)....older rear ends have a single ABS sensor on the diff.....
Are you looking to get a FF rear end?
Depending on your plans, there are also gearing concerns......there is usually an axle code somewhere on the axle....helps to determine gearing, limited slip, etc.
Two more things......(I'm no expert here......YMMV)...there are Danas and Sterlings as well.....and single rear wheel and dual rear wheel versions.
...and a few other differences as far as width goes I think starting at E450
2008 E350 RB passenger 4WD SMB penthouse
2013 KTM 350 EXC
2008 KTM 250 XCF-W
2000 KTM 200 EXC
2003 Honda Element