Top ends are fairly quick to pull apart. How about assembling and running to see if the power is ok for you, then machining the cylinders later if need be? Did the Gilardonis come with the pistons? I would worry most about piston valve interference when altering things. On the big blocks Iíve assembled the pistons come flush with the cylinder top. This is where I would entrust things to my machinist but Iím a lightweight.