pushrod length

What length pushrod would normally be needed in a LA360 with 273 adjustable rocker arms? Thought about putting these rockers on mine since I have them lying around. I have a valve tapping sound. I placed a straight edge across the tips of the valve stems and all of them are not the same height. Figuring adjustable rockers would solve this problem, but I'm not sure what length pushrod I need. The heads have not been cut, but it does have FelPro 8553 gaskets. I also have the 273 pushrods that came with the rockers, but I'm pretty confident they are not the length I need. Can anyone help me out?

Thanks.
Author: admin