Low and behold after digging thru what was a pretty good build-up of rust I found a line of small numbers. For whatever reason the numbering sequence and placement is entirely different than the other 5 I was comparing it to. Looks like its a 489 case. Plan on rolling an early clutch pak unit in and changing the yoke. The one that's on there is in pretty bad shape. Counted the pinion and ring gear teeth and confirmed it is a 3.91.