I think the cam siezed and tore off the aligning lug on the cam and the top timing chain sprocket broke the bolt. That reduction gear for the distributor would have stripped before breaking that bolt.

Another thing, maybe someone was using that bolt to turn over a motor for timing purposes....or? and it broke.

Michael J. Carsner proud driver of "Aint Pretty"

37 boggers, 571 gears, Detroit+Lock-Rights, 20R stage 1 LC Engineering head on 22R motor.
MUD!!! Its whats for dinner!!