Hi Bob, If your current Mustang gearbox is "stock" then it probably has a 0.68 Overdrive gear for 5th. Most of the FOX body cars did. I don't remember just how many choices for OD gears are available, but I know there was at least a 0.90, 0.80 and 0.75.
The reinforcing is actually just a more stout bearing retainer for the 5th gear shaft. I found the site that describes it: http://www.5speeds.com/t5.htm
Next time I have the tranny out of the race car, it's getting one of these kits even if I don't change the gear ratio on 5th. It just makes sense when the only times I'm in 5th gear are when the pedal's to the metal.
You'll note that 5speeds.com also has some nice gear sets for these boxes. Half way between standard helical and straight cuts.
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