Ford 9 inch housing w/oval dimples identification

Definitely a 9", it's been modified with drain and fill points added, and a late '50s/early '60s housing.

 

Thanks Crazy Steve, so the two round dimples on the back of the housing doesn't necessarily mean it's an 8"? Are there any issues with the ring gear actually rubbing on the back of the housing like mine and that's why they made the protrusion for the ring gear in later model housings? Are the ring gears the same diameter for all gear ratios?