Welcome to the forums. :tup: You found the casting number for the pinion support. Unfortunately, that doesn't tell us much. I would first check two other places - on the driver's door edge is the warranty tag of plastic-covered paper. If still there, it should list a code for "axle", and two if it's 4x4. If that's gone or obliterated, look for a metal tag (about 1/2" x 1-1/2") under one of the bolts holding the gear case into the rear axle housing. It lists the info including gear ratio. Post what you can find here, and then we can tell you how to confirm the info, in-case the gears have been changed in the last 37 years.