Well the problem has finally been identified, I pressurized the cylinders and blew air out all three intakes. I didn't even touch the intake cam or shims during this process. It sure seems like I would have felt it when the piston bent the valves, apparently it doesn't take much force. The head is about to come off so I'll update with photos in a bit. Any chance the head is salvageable? The manual makes it sound like the head is completely unserviceable and disposable.