"This causes the ring gear to float on the differential and only the bolts hold it in place. This causes contact pattern problems. I have seen several 12 bolt rear ends that sheared the ring gear bolts off because of a ring gear spacer. Ring gear spacers are a bad idea and should be avoided. "
Yes, these are very old school, but back in the day. Spacers are what we had and I saw a few rears that sheared the bolts off clean.
I had a customer with a 70 Impala with a 427 BBC and 4 spd. Was real hard on drivetrain parts. Sheared the bolts on first drag race..