Rear Differential Gasket 9 Bolt

I have a 63 Signet, Slant 6 that I would like to change the rear diff gasket on. I bought a replacement gasket that has 10 bolt holes, mine has 9 bolt holes. Any idea where to get the gasket???? I think I must have a 7 1/4 rear???

Thanks for the help.
You have the 7 1\4 with the 9 bolts an 8 1\4 has 10 you might try a dana 44 from a dodge pick-up they were small