...and there's the third tolerance. Where the holes are drilled in the camshaft. Stack all three together and you're likely to get very different results from engine to engine. Even the same engine with a cam swap. I think it's best at this point if you're building from scratch, mark the front of the block on the timing cover area where the holes are in the block. Then stick the cam sprocket on the cam and mark on the sprocket where the holes are in the cam. That way, you can line them right up for priming purposes.