Snowman in checking your rear axle ratio I think you missed the part to multiply the drive shaft rotation by 2. That would make your rear axle ration 4.56 more inline with what came in the trucks of that era.
Yes final drive in transmissions is always 1:1, but over drives are not considered the final drive. An over drive is usually 25-30% which would drop your rpm down to around 2k.
Larry
