Dana 44 ring/pinion swap
You'll definitely need to recheck pinion depth and wear pattern to get the shims right for the new housing. The "case splitter" is a device that bolts to the diff cover area and applies pressure towards the hub, stretching the case a couple thousandths so you can install the diff and shims without getting out the BFH and ruining the bearings. As dirtball said this is something that should definitely be done at a shop, and won't cost much compared to the headache you will avoid.
'97 F250HD 4x4 460; '85 Ranger, 350hp 289, T5, firstname.lastname@example.org
"If at first the idea is not absurd, then there is no hope for it.” Albert Einstein