It should be an 8".... but then again mine shoulda been a 9"...

From the rear if the housing is more oval than circular it is an 8". 9's are more circular.

 

I just look at the bolts infront.. Simple rule with them.

 

Most of the mustangs came with 8 inch, except for the HIPO models which had 9's. If you crawl under the car with a piece of paper, just rub the paper up against the casting where the ID numbers are. Usually, it's so darn dirty, you can't read it, and it's in place that's hard to see as well. The paper trick works pretty good - give it a try. Just press it up against the numbers and rub. Then look at the paper. Beats getting a neck strain and grease in your hair under the car!!

 

A simple way to tell an 8-inch from a 9-inch is to see if you can get a 9/16" socket onto the bottom most studs of the 3rd member-to-housing studs to remove the nuts.

If you can get a socket on them, you have an 8-inch. If you can only get a 9/16" boxed-in wrench on them, then you have a 9-inch.

http://ultrastang.com/Rearinfo.asp?Page_ID=1

www.ultrastang.com

 

so would an 8" centersection fit in a 9" housing? or is there even any difference in the housing?

 

Nope...not even close. The housings are different.