I actually did tear it apart originally to mill the head a bit, and clean and enlarge the ports slightly as well as smooth the casting like you mentioned. I didn't port for performance though.
I've been talking with Fabian and he recommends just getting a reed valve. To be honest I'm pretty over all the work on these bikes. I have a shift kit and expansion chamber, mikuni carb, etc. So going through 3 bikes and 4 engines now I think I'm worn out!
2 engines I ported were monsters compared to stock but the cylinder jammed around 900 miles of full throttle on both of them. Although I'm almost positive that it was because I added more oil to the mix both times and leaned the mixture out too much. With an NT carb and stock exhaust that wouldn't probably do it, but with a fine tuned mikuni with pilot jet and expansion chamber I'm certain it did.
I also had no shift kit on those ports so rpms were constantly insanely high and I didn't have the extra speed that comes with gears. I can't even imagine the beast that this bike would be with a ported engine and shift kit. It might actually be too much torque for it.