considering this is a new engine rebuild, i would be putting my effort in to determining if its an engine problem.
as others have stated, sounds like venting, ring or valve stem issue to me.
you could try dropping the engine pipe and looking for oil, but considering the smoke isnt that bad, i would think that any evidence of oil would get burnt away pretty quickly.
im assuming your car is the grey r32gtr with the leather, cant remember the previous owners name, but if it is those 2530s on your car,they have already been rebuilt.