9 rear end bolts, what rear end do I have?

[dart custom]

72 dart custom. 318 engine. I went to buy a gasket for my diff they said its 10 bolts my cover is 9 bolts how can I find out what this rear end is out of ?

 

[Oklacarcollecto]

It is the standard 7 1/4 that is used in your car. The 10 bolt 8 1/4 is optional. It would be a Felpro RDS12775.