white smoke is coolant, not oil nor fuel (those are blue and black respectivly)....no, white is coolant and I would suggest you run it further and longer than a few minutes to allow everything to seat. I could go away with run-in....and it could be residual moisture in the exhaust that hasn't burned off after sitting for a period. I'd run it for 30 minutes and see if it doesn't clear up.....you undoubtedly changed the oil as part of the cylinder head job right? You must change the oil as part of a valve job....