If your cam says it is a .500 lift, the rotate the engine so the valve is closed and put a dial indicator on the retainer. Set it at .100. As the valve opens. The dial indicators pointer will move towards zero. When the valve starts to close, you should have seen how far the pointer went. Minus that figure from the .100. That figure when a 1.5 rocker is used should be in the low .600 range which would show you not only the exact lift but also how much you loosing from the angles of the tappers and pushrods.