The manual for my Hirth F-33 engine says that if it is mounted inverted the spark plug wires need to be secured so they cannot fall off from vibration and gravity. After inquiring on the lonesomebuzzards.com forums George and Dick gave me what I thought was the best idea.
Purchased two s-clips and a 1/4″ diameter by 6″ long spring from the hardware store. Added a scrap piece of fuel tubing to prevent the spring from chafing the ignition wires. Drilled a couple of holes in the cylinder head fins and voila, problem solved.