They can be notched as long as you have at least .150" thickness left. I am going to put a sharpened 1/4" rod in a vise & the support rod for my dial indicator in the vise several inches away & set the dial indicator plunger down on the tip of the sharpened rod, zero it then raise up the plunger & set the piston on the sharpened rod & the plunger down on top of the piston & see how thick the deck is to start with & that's as far as I have gotten with this. I haven't yet found a co that sells a cutter that I can chuck in my drill press & someone welded? several small bars to the bottom face of an old valve & it worked to cut the soft aluminum piston but I dont remember how they did it.