What Pat said.....I've pulled a couple of the 5/16" studs, probably just not enough grip area on the threads or something. My cure has been to go to the 3/8" studs with guide plates, machine the correct amount off the casting, and poly locks on the rockers. Similar set up on the small block in the Mustang, it's been abused for 5 years now and still holding together just fine!!!! Same heads too, Dave--just a lot of porting and flow bench time on them one winter at a buddy's machine shop......