Cast Aluminum Differential Girdle by XPERT PerformanceŽ-- Exact dimensions as Ford Racing unit, but with no logo.
Available @ Amazon.com. I paid $90.00 US dollars.

Fits Ford 8.8 differentials for F-150s, Mustangs, Crown Vics, Town Cars, & Grand Marquis perfectly.
Installs in about one (1) hour.
This is a quality, heavy aluminum casting -- it will strengthen your differential housing for towing and/or racing.
The stock Ford 8.8" differential tries to destroy itself under hard acceleration, towing, and/or heavy bearing load.
This differential girdle casting is THE answer to those problems !!

PARTS IN KIT AS DELIVERED:
1 DIFFERENTIAL GIRDLE ASSEMBLY.
1 PAPER GIRDLE GASKET (not used, see below)
10 FLAT WASHERS
10 LOCK WASHERS
10 CAP SCREWS

NOTE: Before doing ANYTHING, remove the silver paint from the INSIDE surface of the aluminum cover. A spray-can of carb cleaner will do a good job!
If you DON'T take this step, the gear lube will strip off the paint, and the differential action will stir it into your expensive gear lube and SERIOUSLY muck up the gears and bearings !!

DIFFERENTIAL GIRDLE INSTALLATION INSTRUCTIONS:
STEP 1. Remove old differential cover.
STEP 2. Inspect all internal components for visible defects and repair/replace at this time.
STEP 3: Clean inside of axle housing thoroughly and carefully remove any gasket material or sealer from the mating surfaces. If your diff has a magnet inside, clean it thoroughly and replace the magnet.
Before proceeding to step 4, prepare the girdle and gasket -- Install the drain plug, using Permatex Ultra Black on the threads to prevent any leaks. Make sure the load-bolts are backed out to prevent contact with the bearing caps while installing the girdle.
NOTE: The supplied paper gasket was not used -- no more cheap gaskets and messy RTV crap for me !!
I opted for the LubeLocker Part Number LLR-F880 FORD. The LubeLocker gasket is made of steel (blow-out proof), with a rubber coating on both sides. It has an elastomer sealer on both sides that is applied at the factory, and the LubeLocker (made in USA) gasket is re-usable.
The LubeLocker comes with a diagram for the bolt-tightening sequence. USE THE DIAGRAM for maximum strength and NO-LEAK results.
STEP 4: Install the girdle with the gasket, bolts and washers. Bring the bolts up to "snug", using the LubeLocker pattern.
STEP 5: Using a good torque wrench, torque the girdle to the axle cap screws to 25 ft./lbs. , and DO NOT OVER-TIGHTEN !!
STEP 6: Hand-tighten the two load bolts until they make contact with the differential bearing caps.
STEP 7: Torque the load bolts to 90 inch/lbs.--- (7.5 ft/lbs) Excessive torque can (and will!) damage the differential bearings!
Torque the jam nuts to 25 ft./lbs.
STEP 8: Remove FACTORY fill plug, fill differential with recommended lube from the upper hole in the girdle until the fluid runs out of the FACTORY fill hole in the side of the differential housing casting.
I applied some of the Permatex Ultra Black to the fill-plug and drain-plug threads -- to insure against leaks.
I used Mobil1 75w90 LS (for limited-slip differentials) Synthetic Gear Oil -- Standard capacity is 3.75 Pints, (60 Oz.), but the new Girdle requires 5 Pints (80 Oz.).
This unit makes the rear-end assembly stronger, allows the differential to run cooler, and the extra fluid capacity allows for longer change intervals.
After a proper round-trip shake-down cruise across the desert from Phoenix to Palm Desert, Ca., in 100+ degrees, I checked the differential temp with an Infra-Red gun, and the differential runs about 20 degrees cooler than it did with the OEM cover under similar circumstances.
Picture shows the heavy-duty diff cover and LubeLocker gasket installed on a '95 Mercury V-8.
After a 5,300- mile round-trip from Phoenix, AZ to Philly, PA, with outside temps between 104 F and 47 F., speeds between 40 and 105 mph, the bottom of the differential was wiped with a clean paper towel. CLEAN and DRY !!

UPDATE: One (1) year after installation, the differential remains CLEAN and DRY --
If you want a leak-proof gasket, get a LUBELOCKER !!