Take out the plug and preheat the engine with a hairdrier to 150Deg F. Put a dash of 3 in 1 oil in the cylinder and turn over on the box for 2 mins. This is to fush out all the crap that might be there after iot was put together
Replace the plug and preheat again to 150 at least and start.
For running in let the engine idle for one tank and keep checking the temp. You need to keep the temp high or the engine will wear out and not in! Keep the hairdrier on the engine during the first couple of tanks at idle.
My mate has the same engine and has ran it in at temp and has used it for 3 meetings and its still tight at TDC without the plug!!!!