This isn't looking good. The order from Justdifferentials is still listed as processing. After getting additional info, I have tried to get the order shelved until I pull out the rear to see exactly what I have. I can't reach them. Called several times. Doesn't allow me to leave a message. After ordering, I checked reviews and looks like their customer service like this is common practice. I know stupid. Do as I say not as I do comes to mind.
As explained in my other post I wanted something little more drivable. Ordered the 3.38 gears. I was assured this was the correct ring and pinion for my truck. And later finding out the '55 55T comes with various carriers. Possibly not the 9.375.
I have been building rear ends for 60 years and I am thoroughly confused at what you are trying to do. It looks like you have the GM corporate HO33 which was later called the HO35. There were only two gearsets available for these. The GM 3747808 which is a 3.90 and later the 3764960 was available for auto trans at 3.38. I would be interested in seeing what you bought and what you are going to do with it.
