I have a fxt 4.44 that has the rear cover removed. When I installed it, it made a terrible whine and the gear oil came out black after only 5 miles. I opened it up and all the gears look fine.
I also have three NA 4.11 gearboxes that can be used for parts, so if you want a center diff, I've got 'em, just dont know if it's the part you need.
Shoot me a PM