Re: 9" vs 12 bolt.
 

lots of them

Re: 9" vs 12 bolt.
 

I changed from a 9 inch to 9.5 inch Gleason set up. These were pretty common pro stock set ups years ago before they moved on to bigger stuff. Much more efficient than the standard 9 inch

Re: 9" vs 12 bolt.
 

A buddy used one of those 12-bolt drop out pieces many moons ago in a SS application.
He used up gears like crazy, that lead me to believe the performance advantage aspect somewhat disappeared, it was a heavy car
and the Aluminum 3'd member maybe was flexing?

Re: 9" vs 12 bolt.
 

A good test would be to a loss test on the 9” nodular vs the High strength steel that Strange manufactures for Ford NASCAR program the HS case is 3 lbs lighter that nodular and about 30 % stiffer. According to Bob Stange so it hold everything in place. I don’t believe an aluminum case is as strong as the Ford nodular with the modified tail bearing, the Daytona pinion support and a load bolt to support the ring gear.