The motor I'm putting in my 58 came out of my 68 Camero.It's a 350, I broke a rocker stud and didn't think to much about it. A week later I broke another stud. The motor came with the car so I didn't know what was in it only that it had solid lifters and ran really good. Come to find out the cam was .536 lift on the ex and .514 on the intake and it was the ex studs that were breaking.
Found out the stamped rockers didn't have enough slot for that size cam and were hitting the stud and was pushing (bending)the stud. Got some roller rockers -- problem fixed. I have been going through these post's real fast and might have missed it if you said what you found on your rocker problem.