Any chance the rocker assembly got some rockers mixed up?
Only ran for 10 seconds, what procedure was implemented to assure the hydraulic lifters would not be "pumped", there is no guarantee that the oil will come back out of a "used" lifter just by reassembling the components, especially now that different pieces are being used the preload on that lifter will want to be different. That lifter likely isn't letting the valve close.
