Ford you mean ?

If so, easy way to tell is look at it...the couple of bottom mounting nuts (for the center pumkin) if you could put a long extension on them to remove them, it's an 8"....if the pinion support area overhangs (on the bottom) a couple of them, it's a 9"

You can kind of see here on mine what I am saying. This is a Strange housing, but same basic idea..