^ This. Have you confirmed that with all the valves closed, all the rockers are in the same position on the valve tips?
Because if some are further away than others, then that indicates you may have a bad batch of rockers with different ratios. Hughes had a similar problem with their rockers a few years back after a bad batch was mixed in and some of their sets had different measured rocker ratios.
Once you've confirmed the rockers are all good, then you only need to change the valve locks to the lash-type, add the lash caps, and that should fix it. You don't need to remove the heads and you don't even need to remove the springs and retainers - just the locks.