Make sure the cam is on the base circle as that is the only true way to measure for pushrods. TDC is not always on the base circle of the lobe. This may be the reason for the difference in your readings. I measure #1 and #6 so you can get an average for both banks just in case the decks or heads have been unevenly machined. Check it for both banks and get an average length. You will be good with something in the middle with adjustable rockers and a hydraulic cam

Gus