I got a set of 3.42 gears from an 8.6 and the guy said had some bearing noise in the rear. I ask him if 8.6 would work in an72 8.5. He said he put a set in a Rat Rod without any problems but didn't know what year the rear was.
Here is a pic of those 3.42 gears. I would like to trade some one for a 3.73 gear that had little or no noise. The ring gear fit my 8.5 carrier.