I have built way too many engines in my 69 years and can honestly say I have never seen a lock split like that....
I would be changing out all of the studs as well as the new locks, but before bolting it all up, make absolutely sure you are not getting coil bind on those exhaust valves....
Do you know what springs are installed? What is cam lift? Installed spring height? Closed pressure? Open pressure?
If the cam is 560 plus, stock bbc valve springs will equal spring bind/cam death. All the factory springs had far too much spring rate, giving them weak seat pressure and stupid (350#+) open pressure, or simply not enough room for even .500" for the newer stuff. Check your installed height and buy the appropriate single spring.
I have witnessed many times a stud will flex and snap off with coil bind, but have never seen a lock split.
Make sure the top of the new studs is perfectly flat and I always use red loctite on the locks to prevent walking...it is also not necessary to really lean on the locking screws,,,,,just make sure they are hand tight with a T wrench.
