Run it with castor oil in the fuel and a smaller than usual prop, then let it run fast as you monitor the exhaust spray and engine temperature. 1 minute or 2 minute short runs followed with checking the glow plug and bolt tightnesses between runs. When the exhaust residue is clear and the needle is steady, the engine is ready.
I usually use 25% oil for the initial break in.
Run it WOT only at a slightly rich scream. Do not play with part throttle setting until after the engine is broken in.