If you had timed the cam wrong, you would'nt have been able to drive around for so long.
Ive seen your kind of damage a million times. Valve seized in the guide and bent the pushrod. Piston hit the valve and snapped it off.
Its amazing how often this happens with bronze guides, but for some reason, people want them. Bronze guides are very prone to wiping out too. Go with iron guides and dont let anyone convince you otherwise.
This kind of damage was caused by improper valve stem to guide clearance. Too tight. It could be something as simple as the machinist not cleaning the guides out thoroughly and greasing the stems. They leave crud in the guides and next thing you know, a valve sticks. It doesnt take much debris at all to do this. Dont ever let your machinist knurl a guide. Get new iron ones put in and make sure the guides are reamed to a perfect clearance. They need to Mic the stems in 3 places on all valves. Some guys get lazy and dont bother. The guides MUST be spotless clean by blowing them out with carb cleaner or brake cleaner, and then use a simple lithium grease. I watched a guy ream guides out all the time (my old job), and he would ream them without blowing out the debris first and didnt even use cutting oil when he reamed them. This guy didnt last long cause we had quite a few junked motors returned to us after dropping a valve. He was an "expert" who had been doing cylinder heads for 20 years. Amazing how all the years of experience dont equate to a good machinist, ever. You got it or you dont. Another thing that kills guides like this is when the "machinist" machines the top of the guide to accept a perfect circle teflon seal, by using a special cutter that mounts in a hand drill. They ram the pilot of this special tool into the guide, dont use oil, and destroy brand new guides cause they wanted to do it by hand and save 5 minutes. This happens ALL THE TIME. Even the best get lazy, and you end up paying for something in worse condition than when you brought it in. Another thing they do, is they dont machine the top of the stem of the valves. They are rolled over a little, and the valve doesnt slide into the guide cause of this lip. So instead of machining the end flat and grinding a chamfer, they hammer the valve in and destroy it. There are so many things Ive seen people do that would make a customer gasp in disbelief. Just cause a place has a good rep, dont trust everything they do. You need to understand what they're doing and watch every bit of it. Just because they appear to me meticulous and taking their time, doesnt mean they are.
Anyway, I would replace all your guides with iron ones and get the clearance perfect. Everything must be spotless clean and done right.
. I was wondering who else has had this happen. The heads had right at 700 miles on them, from new, not rebuilt. 
who has a roller 218 in his car with GN1s and set the roller cam on the wrong dot . Easy mistake. well luckly the motor didnt fire but it did break a valve ,Guess which cyl ...... and bend a few . Anyone can make a mistake .
