I've been tracing some differences worth mentioning between various 9 3/8" rears. First, a recently discussed issue concerns the 67-70 big rear asking if a 3.07 posi carrier can be used with a 3.42 gear. The answer is NO, at least not without a ring gear spacer. My 67 Riv has a 3.07 gear. I spotted a 70 Riv with a posi this week at a local yard. I removed the posi, and grabbed the gears also since they were 3.42. I was planning to install this posi with my 3.07 gears, not really wanting a 3.42 for the highway. Good thing I grabbed the gears, because the carriers are DIFFERENT. This actually makes good sense because with the 71-75 big rear, the 2.73-3.23 carrier is different from the 3.42 carrier. See in the picture, the gear mounting flange is a different height. These are both 67-70 carriers, the posi was used with a 3.42, and the open carrier was used with a 3.07. They are different. I will go ahead and use the 3.42 gears so that I can make use of the posi, and run some really tall tires to tame it.