8 3/4 rear question

Posted this on B-Bodies Only, but thought I'd post it here as well...
My brother has an 8 3/4 rear out of an 68 Charger origionally a 318 car (honest). The center section has no markings or casting numbers on it. Has anyone ever heard of this? If so, what rear (pinion Diameter) could it be, 741, 742, or 489?