Yeah........spring upgrades are often overlooked.....old springs can lose there spring so to speak, but when they break they can do major damage and sounds like it did. Strip it down completely and have the block checked, most likely the cam is wiped on that lobe as well. after checking the heads from seat cracks or damage from the valve, have the heads machined for fresh studs. Might be cheaper to buy another set of heads. Man hope you get it sorted out.....awfully expensive when this happens. A pre race inspection i always perform before I hit the staging lanes is to pull the valvecovers of and give a quick look at the springs, and retainers..........It might sound odd but it gives me a little piece of mind before I pounce on it. Hope this helps