Yo Kris!! I researched this pretty hard before I bought my 3.73. As long as its an 8.8 it will work which includs most F150 trucks also. The problem is most used ones dont have a better ratio than what you all ready have and junk yards want to sell the whole axle assembly not just the ring and pinion. I got mine off ebay used for 40.00 and a bearing and shim set for 69.00. Lex
About the largest you will find in a stock mustang will be 323's with most being 273 or 308's. All the 8.8's used the same gears but the trucks used a heavyer spring on the clutch paks so be aware if swapping entire diffs.
I used the truck springs (along with an extra set of clutches) on a Trak-Lok rebuild for one of my Mustangs several years back. Supposedly made the rear lock up better: I don't think the truck diff is anything to worry about.
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