Re: Different 9 inch housings?
seen many 9 inches, and the one you have will fit.
The biggest issue you mention is the brakes. The LTD has discs and you have drums.
Now your drums may go straight on (its all to do with the mounts welded to the diff), but the better option is to fit the discs.. 4 wheel discs beats rear drums every day. You will have to use the 78 model units anyway. Just remember to fit the correct master cylinder.
Sure this is a bit of stuffing about, but its all bolt on, so not rocket science.
Oops another thought...the diff is out of a 78....the year they started making XD's...it won't be that different!