I think you just found the c-clip. It's in the
oil pump. The crank drives the cam, the cam drives the distributor, and the distributor drives the
oil pump (through that twisted rod). It looks like your
oil pump seized and that rod is designed to twist and break rather than cause even more damage. The valve tip/retainer/locks are correct. It's hard to tell from the pictures why the bottom of the rockers hits the retainer (what you call the valve spring cap). I would replace all the lifters, rockers, and push rods, as well as the oil pump and drive. However, as you said, let's hear what Eric has to say.