I didn't catch above if you were going to be taking the heads off, (I am assuming you are,) so I think you will get a good picture after the springs are off the valves. The valves will either slide in the guides good or they won't, and a simple "wiggle" test will at least give you an idea on how loose/tight they are.........then you can actually measure them with some sort of measuring tool.........maybe when they get hot they expand, and tighten up.