Capacity, for the 8.8" ring gear version, is 1.5 litres (or 3.25 pints). For the 7.5" ring gear, capacity is 1.4 litres (or 3 pints).
From the 1994 Ford Service Manual:
All conventional axles use Motorcraft Premium XY-90-QL (ESP-M2C154-A) lubricant or equivalent, plus 4 ounces of friction modifier additive EST-M2C118-A (C8AZ-19B546-A) or equivalent for Traction-Lok axles. Always fill rear axle to bottom of filler hole.
Keep in mind he said 3.25 pints and not quarts. You'll only need to buy 2 quarts when you go get it and you won't use it all then.
Former owner of 94 Bird with DOHC 4.6L swapped from a mark VIII
2011 CTS-V Wagon
1968 Torino was an original 289, C4, fully documented numbers matching car. Now: DOHC 4.6L/T-56 swapped, Cobra intake, IMRC delete, BBK long tubes and H pipe. Dynotech Aluminum Driveshaft, 9" rear with TrueTrac and 4.11's.