My 9-inch was out of a 80's vintage Granada and was the correct width. Both the Ford Granada and Lincoln Versailles used a 9-inch rearend.
The VAST majority of granadas came with 8" rears, so you got lucky!
The Lincoln Versailles had the old, HEAVY, troublesome, expensive rear disks. There are FAR better setups nowadays, so it's good to hear you used a standard rear and stepped up to some better brakes.
ps... I've had the stock 8" housing, two 57-59 Ford housings, and finally the Currie housing under the mustang.
I've used the following 8" gear ratios... 2.80, 3.40 and 3.55.
I've used the following 9" ratios... 3.00, 3.25, 3.50, 3.70, 3.89, 4.11, 4.30, 4.33, 4.56, 4.57, and 4.86
These have been used with open carrier, 2-pinion trac-locs, 4-pinion trac locs, Detroit locker and spool diffs. The 2-pinion units are weak, the 4-pinion are surprisingly strong, the DL is super tough, and the spool will pinch the tubes in slicks and street slicks when driven daily around town. Trac-locs will smoke the clutches and turn into basically 'open' diffs if one tire is spun too hard much at all.
The 57-59 9" axles are very tapered and extremely weak. The 65-66 8" mustang axles are far stronger. The 'home made' 31 spline axles are a little stronger, but not trustworthy. Aftermarket 31 spline axles have held up to everything I've dished out so far... as has the Detroit Locker and OEM Ford 'N' case/Daytona pinion support.