Push rod clearence

Pushrod to head clearance should always be checked. Changing to more rocker ratio can do this too. Be careful that you don't remove too much from the 'sides' of the pushrod hole (tube). That can limit what you can do with the pushrod hump, how wide the port can be made (porting) at that point. Really only need to relieve on the intake and or exhaust ends of the hole. Drilling removes material on all sides (all the way around). Best way is to use an endmill cutter and mill the hole wider, on the intake and exhaust ends of the hole only. Almost like a semi slot, you lengthen the hole slightly. If you don't have access to this equipment you can do it by hand with a die grinder and a sharp carbide cutter. More time consuming but safer than just drilling them out to larger size. If porting is not in the future plans or not a consideration...then drill them. Sometimes the best ways are not the easiest ways...that's why they call us 'Hotrodders' a dying breed we are. Good luck, Terry.