push rods on gx 390

Does anyone know how I can measure how long my push rods need to be with out using a push rod measuring tool ???????

I have stock length lifters and longer valves and Iam using the Manton 1/4 O/D push rods and Champion shaft Rockers from Vegas I need to know what length they should be
If you know how to see what the proper geometry you need, you could make a push rod out of a pencil or 1/4 wooden dowel, shortening until its right, then measure what it needs to be. If you are unsure as to how to determine proper valve train geometry, Im not sure how to explain it. Pushrods for the 390 typically come in std. length and .100 shorter from most racing aftermarket part suppliers. Make your own are also available. Others better than me may be able to explain this better. Sorry. Good luck.