This engine has clearance fit on the valves and pistons. If the valves are not completely closed the piston will hit the valve and close it. Leakdown test is a good idea. Cheap diagnostic that will isolate the problem. Go from there. The car not starting because of valve lash being wrong is not good. Most likely they where tight rather than open. Possibly on number one cylinder one of the valves was too open and contacted the piston and damaged the valve. The shop is giving good advice.