Dave,
It's an excellent idea to run any engine on the ground, away from the flying field and all it's distractions and temptations, before you fly it. Any new engine or used one really ought to be sorted first at home on a test stand.

I use scrap wood to make a very solid, strong motor mount. Most are just a slot cut into a piece of 1x6, for the engines that're bolted into your everyday beam mounts. I've also made a setup that will take motor mounts bolted to it so I can mount the engine on the mount that's going into the model. But whatever works for you.....

Just make sure that the entire rig is solid. My pieces of 1x6 are held to a heavy bench with a through bolt and a C-clamp. And they've all got a couple of eyelets to rubber band a tank solidly in place.

Almost every engine benefits greatly from being first run somewhere other than at the flying field just prior to it's first flight. You're not chomping at the bit to fly and if the engine is a little balky at home, you have all the time in the world to sort it out. At the field, you'll be pressured to stick the sucker in the air. And at home you won't have the "experts" gathered around telling you, "it sounds good enough to fly" when it sounds like crap.

A decent test rig is worth it's weight in gold..... if you use it, that is.