Got a Cox reed valve 049 engine going today, with a Davis head.
For a motor stand I'm using a Tatone stand with a piece of 1/8" angle iron on which the engine is bolted.
Don't do this, unless you want some practical education in resonances. At the 'bad frequency' (which was just a bit lower than what the engine really wanted to do) I could see the cylinder moving through a 1/4" long arc.
But I could damp it out by hanging on to the engine, so I verified that it runs (and smells) normally for a little Diesel conversion, and I have the compression and mixture at a good setting to go on a plane.
Tomorrow I go flying.
Sometime soon I go get some nice thick T-bar and make a new test stand adapter for 049s!