Slim chance of the valve and piston not making contact, depends on what rpm the chain broke at. Pull the valve cover, look for excessive valve lash ( indication of a bent or stuck open valve), or if you have it that far torn down, go ahead and pull the head, is the only and best way your going to be able to tell if they made contact.
Since it broke at 70, your looking for a new head. Dont bother just putting valves it it cause they usually crack the valve guides too. When you get another used head, do yourself a favor and put some valve seals in it, you'll thank me later. Make sure to check the pistons to make sure there not too banged up, a little indentation wont hurt but a lot will.