For the valve to drop completely into the cylinder would require the piston to be down a distance greater than the length of the valve.

Mostly, pinning the valves in place with the rope makes it easy to put the springs back on.

If you have the proper spring compressor, it will be a snap.

Read tech's guideline for setting the valve lash. You can probably get it done five minutes a valve, after you get practice on the first few.