Like I said, if it has a bolt on rear cover, it is not an 8" or 9". The 8" is basically a baby 9". It has some strength is properly built, but is really not ideal. If it has the cover, I guess it could be a 7.5", but I really doubt it, so logic says 8.8". What are the markings and are they stamped on a bolt on cover, a tag, or stamped on the rear of the pumpkin housing?
Try this:
What rear end ratio is in my Ford , do I have positraction? - Drivetrain.com