I am in the process of going over my new Promaxx Big Block heads before bolting them on. Just quick "shade tree" techniques for checking guide clearance, valve seat concentricity and upgrading to beehive style springs and retainers. I'm giving the valves a quick "lap in" because I was able to see a little bit of daylight between a couple exhaust valves and their seats under close inspection. All in all they will be a huge upgrade over my 906's.