Ring And Pinion Install

Give some more info on your car (auto or manual? mods? plans to supercharge in the future? etc.). I'd say it's unlikely that 3.55s are the best choice for you, but I may be wrong.

Assuming you haven't bought them yet, I'd buy the gears and master install kit from Tousley Ford. With that many miles on it, and since you'll have it open anyway, I'd replace everything. The master install kit has EVERYTHING you need. Both diff bearings, pinion bearings, axle bearings, crush sleeve, marking paint, all seals, and shims needed. You won't need any other parts with this kit, and best of all, it's dirt cheap compared to most other retail kits ($200 for gears and install kit). Plus it's FRPP brand stuff. Links here and here.

Two issues with the rebuild kit, though: DO NOT use the supplied gasket. It will leak. Guaranteed. Use grey RTV instead. Also, DO NOT use the FRPP axle seals. They will also leak. Go to your Ford dealer and buy FORD axle seals (not Ford Racing). Ask me how I know these two things....

A ring and pinion install really isn't as hard as people make it out to be. I was always under the impression that it was something to only let the "professionals" do, but I really had no issues doing it myself. I've done 2 more since then, all without issues.

Tools that are REQUIRED:
-Dial indicator for measuring backlash, and a method of holding it (I've got a magnetic block purchased from Harbor Freight, works perfect)
-Gear marking paint for checking tooth contact pattern (should be in the FRPP full rebuild kit)
-Ft-lbs and inch-pounds torque wrench. I've got one of each from Harbor Freight (Pittsburgh brand) that have worked flawlessly so far, and was only like $20 for the two, haha
-Some method of cutting the diff bearings off the differential. Maybe yours will be better, but mine had to be cut off. I used a cutting wheel. Maybe others use something different, but this was a pretty aggravating part of the install.
-Some method of pressing the differential and pinion bearings on (4 total). Don't beat them on with a hammer, as that will damage them.
-Slide hammer to get the axle bearings out. I REALLY had to beat on mine to get them out.
-Plus an assortment of other regular hand tools (ratchets, sockets, wrenches, etc.)

Also, probably the hardest part of the install is getting the pinion depth correct. The general procedure is: install pinion, install differential, check/adjust backlash until it's acceptable (via shimming the differential), check the contact pattern (there's charts online showing what's acceptable), adjust the pinion depth accordingly if contact pattern isn't good (via shimming the pinion), and then repeat the process as many times you have to until you get both correct (backlash and contact pattern). The problem with this is that the shim(s) for the pinion are behind the large pinion bearing, which has to be pressed on / cut off. So if you don't get lucky with the pinion depth the first time, you're going to waste a bearing every time you have to change the shim. The way I addressed this is go to your local parts store, and get another pinion bearing (have them cross reference the part number on the one in your kit), the cheapest one they have. Then take that bearing and very slightly ream out the inner diameter so it can freely slide on and off the pinion shaft. Use that modified bearing to do all the checking when you change shims, then once you get it figured out, press the actual bearing on.

General notes about having a good install: the most important things are the contact pattern and the bearing preloads. Contact pattern is a little tricky because it's pretty much guess-and-check until you get it right. Correct bearing preloads are CRITICAL if you don't want the rear end to make noise. The differential should be in pretty tight; it definitely shouldn't fall out on it's own with the bolts and caps removed. I added a .001 shim on both sides of the diff after I got the backlash correct to tighten it up, and haven't had issues with any of the rebuilds I've done. The pinion is preloaded from the crush sleeve. Be warned, it is a BEAR to crush down. I had a 24" breaker bar, and it was all I could do to crush it down. But you want the pinion to be preloaded a certain amount, I think it's around 20 inch-pounds. Which means when you put a torque wrench on the pinion, it takes around that much to actually turn it. As mentioned before, it's these preloads that keep the bearings from making noise and whining.

One last thing, on the gear oil. If you can find it, get gear oil that doesn't have friction modifier already added in, and get a bottle of Ford friction modifier. I think I used Mobile 1 75W140. It may not make a difference at all, but I've heard that the friction modifiers already in the oils can cause small issues with the Ford rear ends. May not be an issue at all, but it's easy to not take a chance at all, especially considering there isn't a cost difference.

I also like to add F150 springs inside the diff with the carbon fiber clutch discs. The F150 spring is a little stiffer and, they are cheap. Also, soak the clutch discs in the gear lube you are going to use over night.