9" axle spline count

[California 72]

Understanding there are different spline counts for the 9", wasn't there a standard for the Mustang at any point in '71 or '72? Trying to keep the car drivable until the parts are found so opening things up just to check is a bit more work than I'm willing to create. I'd like it to be a "one and done deal" for the rear so the mustang doesn't stay corralled for the remainder of the summer. Heck, it just started a couple days ago! I'm going to try and grab the differential tag to see if it can help. Any help would be appreciated. Thanks!

 

[Hemikiller]

The vast majority of 71-73s were 28 spline. All 429, Boss 351 and 351HO cars were 31 spline. Some M and Q codes appropriately optioned were supposed to be 31 as well.

A 72 H-code like yours should have been equipped with a 28 spline 9" rear axle, using either a 2.75 or a 3.25 rear gear.

 

[California 72]

Hemikiller, Thanks for the info. Couldn't find the Diff tag. Other than the buck tag, whatever is stamped in sheet metal and the newly uncovered door tag (painted over by the family of the original owner prior to auction) all other tags are missing.
And yeah, the door sticker shows the "2" code, 2.75 open. Really hoped it was a "K" before uncovering door tag and after a really lucky burnout test where both tires lit up but sadly, just not to be. Would've saved me from buying the whole 3rd member.