You should have your intended springs on the heads, not checking springs. You also need to have the lifters that you'll be running. The solid lifter and checking springs, that's what you would use for degreeing a cam, but for measuring pushrods everything needs to be installed as you're going to run it. Push rod measurement should be the last thing you do. .. sorry if this is kind of long-winded... Put an adjustable rod in, at it's short setting. Roll the cam until the lifter is on the base circle (the backside of the lobe). Bring the rocker adjuster to where your desired number of threads are showing, closer to zero is better with today's ball-end adjusters. Now unscrew(make longer)the pushrod until you have zero preload on the lifter, and are just seated in the rocker. It's a feel thing, but with a light and good eyes you will see if you begin to compress the lifter cup at all. Some guys lengthen the pushrod while gently they spin it; it will tighten up when your getting the slack taken out. When you're confident you're at zero, with the pushrod end fully seated in the rocker, take the pushrod out, being careful not to change its adjustment, and measure its length with your 12" caliper or dial indicator. Then simply take that number, and add your desired lifter preload to it, and that is your measurement. It's a little bit of work and take some time but it really is best to do each valve, and you can then compare them. If there are slight differences, no big deal you can afford a little one way or the other in your preload or by adjusting the rocker a small amount. If there are any big differences between them, you would order different length pushrods to suit.
Sorry, I don't have a rec on a cam button though...
