Looking at that car, almost a shame to change it, but why not! Just makes it better.
A 9" may be overkill, the 8" is a good compromise - that is if you can find one. I 'ended up' 7-8 years ago with a 9" simply because I just could not find an 8" that wasn't so rust pitted that it was well weakened. Also, the 9" has probably many more choices of replacement gear sets.
With that blather said above, another choice is the Ford 8.8 rear ends. Very available in salvage yards. Are 56.5(Ranger p/u & early Explorer) to over 61" (Crown Vic, etc) wide, depending on the source vehicle. Many have disk brakes, gear ratios go from the high twos to the low fours. Every part is still available at your local parts store (drum brake parts for an 8/9 incher are virtually impossible to find at 'local' stores)