Easiest way to get the springs/valves off head.

[Goat Blower]

You just have to make sure the piston is at TDC for the valves your are working on. Turn the crank 180 degrees and repeat, no dropped valves. Although to be able to put the springs and retainers back on, you'd need the valves completely closed for obvious reasons, hence the use of air or some rope down in the cylinder.