That's the part number for the housing. To find the ratio, you have to wire brush the underside of it until you see the numbers Justin listed stamped into the metal. You can also tell by the color of the nut holding the flange on. White, yellow, blue on the 5 speed rear ends, but off the top of my head, I can't tell you which color is which ratio. Basically if it came from an 8 its 3.08, if it came from a TR7 coupe, its a 3.90 and if it came from a vert, its a 3.45. Spin the input until one of the brake drums spins one complete revolution and count how many times the input spins. Thats you ratio.