Rear axle leak ...

Hello everybody.
I have a right side rear axle leak and I think I need to change the oil seals. Problem is I'm not sure what size is this rear axle. The car was originally a slant 6-225. Can you enlighten me on the subject ? I think the different sizes are 7 1/4, 7 3/4, 8 1/4 and 8 3/4 …
Thank you so much for you help.