You'll have to use a degree wheel and a dial indicator to do this correctly and accurately. As you pointed out, the initial opening and closing events are happening quicker than your eye can detect. And the lifters being preloaded is also causing errors in your readings. You also have to have light tension checking springs in place of the valve springs as well or you'll never get there.
So I really can't read the stock cam until I do a head swap on it and can swap out the check springs during an initial install of the head (using ARP head studs), and can check the cylinder pressure and cam timing then. At that point I can disassemble it and advance the cam if I need to, and put the stock springs back in for final install of the head/intake/carb/exhaust.
