Damian,
I would run the engine as it is for a few hundred miles more, at least till your first oil change. Have someone check the color of the smoke for you, starting up, driving normally, and going down that hill. You know: white = coolant, blue = oil, black = fuel. Watch for oil and coolant consumption. As long as the car runs all right, there is a good chance to problem will go away. Let the re-builder know of your concern though. If the engine runs badly, none of the above applies.
Bob S.