Nine inch with discs
 

Just out of curiosity, did Ford make any car that came w/ a nine inch and discs as well as posi.? I'm going to drop one into mine and I would like to have some discs on the back. Any info. is appreciated

The Lincoln Versailles came with a 9in rear w/ discs that will fit a Mustang. I personally have one out of a 79. It's a little narrower than a standard Mustang axle so you can also fit fatter tires =) You'll more than likely have to swap the thirdmember to get posi... check my webpage out for some pics and stuff.
http://members.xoom.com/Jefrezicus/

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1967 Fastback, DSS Racing shortblock, Lunati Cam, TFS Heads, Tremec TKO, basically the works... =)

You could also buy a rear disc conversion kit from Stainless Brakes or a similar manufacturer. Price runs about $800-$900 (!) but it gives you everything shiny and new.