Yes, you definitely need a valve spring compressor to get the locks and springs off.
But, to hold the valves from falling down you can use the shade-tree method of pushing a piece of rope or cord into the cylinder. Get a 3 ft piece of lawn mower starter cord or similar, turn the engine until the piston is down, and push the cord into the spark plug hole, leaving a little bit hanging out. Then turn the engine to move the piston up and compress the cord/rope against the head and the valves. This holds the valves in place quite well. Repeat on all the cylinders.

DG