you're talking swapping tcases on the back of a 5 speed?
I think you can swap the guts from a 4 speed into a 5 speed tcase to get a slightly lower low range, but there's something to do with an oiler for the crappy afterthought 5th gear on the h55f which isn't on the 4 speed tcases...so they aren't a direct bolt on.
Or, so I've heard, never messed with that myself.
There'll be experts in the 60 series section, and one in particular (
) in the diesel section.