I have heard that the outside ends of the axles, right near the center, have 3 dots cast in if the axles are 31 spline.
Worth a look.
The Stang more than likely has 28. The truck could go either way... so I would check the truck first.
Worst case, pull the chunk from the truck. It doesn't take much when you get the process down.
Good luck
Dave
Edit:
Houston... We have a problem!
Wasn't 81 the last year for the 9" rear?
I thought they went 8.8 in everything after 82, correct me if I am wrong...
Worth a look.
The Stang more than likely has 28. The truck could go either way... so I would check the truck first.
Worst case, pull the chunk from the truck. It doesn't take much when you get the process down.
Good luck
Dave
Edit:
Houston... We have a problem!
Wasn't 81 the last year for the 9" rear?
I thought they went 8.8 in everything after 82, correct me if I am wrong...
.According to this chart from West Coast Differentials 8.8's began in 1983 but the 9 inch continued until 1986 so there is some overlap. http://www.differentials.com/pdfs/39.pdf I have taken about 30 of them apart at the wreckers and one from a 67-72 series truck was 28 spline but anything newer was 31 spline.It would seem like 28 spline axles in a mid 70's to mid 80's truck would be rare.