If it's Ford, I seem to remember that 9" can't put a straight socket and extension on the bottom nuts but a 8" will let you.
It's 9" Ford. All 8" have a smooth rounded curve over the output shaft and what was mentioned about the fastening bolts above.
looks like a 9" from the shape of the gasket, etc. but the ribs are a bit odd. A straight on shot from the front would help figure out what specific center housing it is.
He is correct,it is a 8". 9" Fords are dropped down where you can not get a straight socket on the bottom 2 bolts.
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