Don't quote me on this but I want to say that the internals in the 4R are stronger. Not sure what makes them stronger. AlJay has a 4R in his obs and i think there are a few others on here. I think all you have to do to swap is to change out a few sensors. I'm sure others will chime in.

 

i think i remeber my trans guy telling me the planetary gears in the e4od are aluminum in the 4r100 they are steel

 

Jeeze man the 4r has all the good stuff in it that you would have to upgrade in the e4od . Putting a 4r in an obs is plug an play no sensor swaping.