I can only find 2 Mustang codes that start with "WO". One is for a 2.79:1 ratio in an 8-inch rear for a '67 model. The other obviously isn't it, because it's for a 7¼" integral rear for a 6-cylinder Mustang.
Do you have a camera you could snap some shots of what you have and post them?
www.ultrastang.com
I have all the Granada/Monarch/Versailles rear end codes, and the code you listed doesn't match any of them, so it's got to be from something else.
It's easy to post a pic if you have a digital camera. Just load the pics to your computer --most likely "My Pictures" file.
After that , you can go to www.imageshack.com to "host" your pictures (for free).
It will be best on the photo size selection at Image Shack, to select "600 x 800" for best picture clarity and for best viewing size of screen.
This is true. However, if it's from a Maverick, it will be very obvious since they are even narrower than the '65/'66 Mustang rear ends --'65/'66 Mustang housing (not including drum assemblies) is 52¼" wide from the inside of the end flange to the inside of the other end flange, where the drum backing plates bolt onto the ends of the housing's tubes.
If the rear end meaures less than this, then you know it's from a Maverick.
Pinto/Mustang II 8-inch rear end would have 4-lugs instead of 5.
www.ultrastang.com
Mav rear end is ~56.5" wide, wheel-flange-to-wheel-flange. Remove the drum brake hardware/axles, and that would give you a bare housing width of ~51.5".
www.ultrastang.com