I would check a few other things for level like the ground it sits on and put the level on the radiator support to see if it is level and also keep in mind that a builders levels are pretty generous of what level is, I put a little more faith in a starret precision level like machinist uses for leveling cylinder heads. I dont expet you to go out and buy one, but I would make sure you have exactly the same bubble on the other reference points that you have on the intake manifold