many many years ago, circa 1972-1973 I used to file notches in the top of the piston on my Yamaha 350 twin cylinder motorcycles to advance the port timing. This allowed me to advance the port timing a little. i filed each notch to be the width of the port and angled it gently. it worked great at the time, as a couple of guys with hopped up Honda CB750 fours couldn't outrun it. I could stay with them at WOT no problem. it did require checking the ignition points quite often and making sure the timing was just right too. it used to urk those two fellows to no end. One of them figured out a way to bore out his engine more, but even then he couldn't pull away from the little Yamaha 350.

so anyway to avoid trying to cut the ports higher on a ABC cylinder (which will result in the chrome peeling off at the ports), I would consider notching the piston to advance the port timing. But you need to check the piston crown and side thickness there on the piston though to ensure you have enough material to be able to notch it a little. You could also put a shim under the cylinder sleeve to raise it slightly too. with a glow engine you don't have to deal with igniton points et cetera. I guess they don't sell the pistons separate from the cylinder sleeve, so one could machine the ports if they really want to and see what happens. it isn't like you are flying inside the airplane yourself.

I had notched the intake and exhaust ports on the piston to advance both the intake and exhaust port timing.
ref http://www.scribd.com/doc/9726341/Tw...ormance-Tuning