I didn't need a spreader when I re-geared my 10.25 axle. (from 4.10 to 3.55). Pry bar to pull the diff, and BFH to re-install. You will need a dial indicator and some sort of mount to measure the backlash with old diff, and then shim the new one 'til it is the same. While I was re-gearing, I went from the factory LSD (whatever the marketing people call it) to an ARB air locker. The air locker came with a shim system that has heavy telescoping parts that the thin shims fit between. This makes it easy to avoid damaging shims when you are trying them out. It isn't a lot of fun wresting the diff in and out under the truck...but the cluttered state of my garage didn't leave enough room to work on the axle indoors, and it was safer from theft still bolted to the truck!
A working friction type LSD is a hazard on icy roads, IMO. Yes it will get you moving, but both rear tires will tend to lose traction at the same time when on ice. This can cause loss of control when cornering braking, or accelerating...pretty much anything other than coasting in a straight line. The effect is very pronounced in a pickup with an empty bed. Weight in the back helps, and it gets better as the friction plates in the diff wear out. (making it closer to an open diff) Running in 4x4 helps also, as it helps keep the rear axle turning the same speed as the front, so you are less likely to spin or lock the rear axle.
This was the main reason I went with the ARB: Traction when needed, predictability of an open diff otherwise.
The ABS/speedometer tone ring wouldn't fit the ARB diff. as supplied, so I had to machine a step and cut a keyway on the ring gear mounting flange of the ARB. That is something to look into with any replacement diff.
I also regeared my D50 TTB front axle. (but stayed with open diff) For this I improvised a spreader using the frame of my 12 ton shop press a couple large turnbuckles, and plates I fabricated to attach to sides of the axle housing and engage the dowel pin holes. Shimming the front was a pain, because IIRC, the shims go under the inner races, and it is hard to pull the bearings for another try without destroying the shims. After a couple tries, I honed out the old bearings to a tight slip fit, and used those to find the right fit, then swapped in the new bearings at the end. Same deal with the pinion, but you needn't mess with that if keeping your old gears.
If you want more traction up front, the options for a D50 are limited. The ARB is available, as well as a couple of "hard" lockers. It may be possible to install D44 diff in the D50 housing, using D50 gears, which gives you more options, such as the Truetrac. See here:
TheDieselStop.Com - www.thedieselstop.com That link is missing pictures and so is tough to follow. It was based on a solid (not TTB) D50, but I know that the TTB and solid D50 use the same diff and gears.
Edit: Here is another thread from the archives where I guessed at how much labor to change gearing. Changing just the diffs would be a little less time, as no need to shim the pinions and check contact patch:
http://www.thedieselstop.com/archiv...64&page=13&view=collapsed&sb=5&o=&fpart=1.htm
Edit: Found a better link for article on how to install D44 diff into D50 case:
http://www.thedieselstop.com/contents/getitems.php3?Front Diferential Limited Slip