Morten,
I have a Magnum 71 and I'd recomend that if this is in fact a ring'd engine you should try to run it on a test bench (or in my case a plank of wood with an an engine mount cut into it ) first for about 30 minutes then transfer it into your plane. The only reason I recomend using a stand for break in is thet if the engine malfunctions there is only a small chance of it getting away from you and injuring some one (or you) in the process. Also if you can buy a tach, It will re pay itself in the long run.

Hope I helped
-Chris Larsen Member of The Livermore Flying Electrons