A 555/A 568 diff. is open on the ring gear end, the ring gear is actually the end cover for the diff assembly.
If you seperate the diff from the ring gear, the axle gear isn't contained inside the diff carrier. (see pic above)
All the other diffs are "self contained" and when unbolted from the ring gear both axle gears stay inside.
520 can be 3:85 or 3:50 but all 555/568 are factory 3:85.
Hybrids can be built but along with the ring gear the matching int shaft must be used.
As mentioned the 1989 minivan 555 is the same as a 1987-88 car unit, where 1989 car 555 is a bit different inside.
To build a hybrid 1989 car 555 requires 523 parts.
Thanks
Randy
PS: Along with close ratios another 555 benefit was the use of 4 pinion gears (spiders)
Not all received 4 pins but that's the reason the diff is built using the ring gear as the end cover.
The one above is a 2 pinion, a 4 pinion has another 2 pinions (spiders)
PS: Have you gone down to the basement yet?? JK
While searching for some diff pics I came across this thread!!
http://www.turbo-mopar.com/forums/sh...ght=A+555+DIFF