push rod length if stock with all stock part with only to a RV cam change the stock push rods should be fine . its when you change the length by machine block / heads valves . thing can change. as well as new parts like longer valves .roller rocker arms. bigger lift cams . roller cams /lifters .small base cams.after market heads the push rod cup can be hirer up in the lifter and use short push rods . many ways to check valve train geometry . i do it by mid lift and have a tool that puts in to play the rocker arm i and using in the build .there many cam books that will show your were contack point needs to be as the rocker tip cross over the valve stem . at base of cam that is no lift it should be to inside of valve stem face .then at mid lift center full lift to out side of stem . i can not cut in past someone may post a photo of this for you . for test you will need a lifter that is sold or use a very lite test valve spring hyd lifter can collapse in testing and give you a false reading .a checking push rod for size many sell them . then a way to measure the pushrod for the right over all size for new push rods
