Sorry guys, I hate to do this, I thought I would be able to find the answer, but so far, no luck. I have GM rear end in my '51 Merc that I need to ID to be able to buy parts…specifically a u-joint at the moment. I know that it is a second series 7.5/7.625 10 bolt, but I can not for the life of me find out what it came out of. The assembly code stamped on the passenger side axle tube reads FC 6K214. The casting code on the bottom front of the carrier reads 551635. I know the gears have been changed out to 3.73(?) from 2.something and I think that swap may have required a different carrier….so the carrier may not be as originally equipped. I have been unable to find any charts with these codes listed to tell me what the rear end came out of. I had assumed the rear end came out of the same '85 IROC Z the engine came out of, but I can not confirm that with the codes I have. Here's my bottom line dilemma: I have to have a drive shaft made and the shop needs me to confirm that my yoke is not bad since the driveshaft gives them reason to think it might be. He asked me to get a new u joint and check for play between the u-joint and the stops on the ends of the yoke. Problem is I've been unsuccessful at trying to ID what the rear end came out of so I what year/car to ask for a u-joint for at the parts store….since the 18 year old working the counter is only going to know is what the computer tells him….not that I have a GM rear end in a '51 Merc.