Very good question.
   For your application, the difference from your CT cylinder to a play port, there's a lot left on the table the ex port can be higher and wider, there's a point when too wide is too much and it will effect piston life. Diffrent bore sizes change this spec. Ex port height controlls the power range, Head and transfers control power curve. The transfers don't get a lot of attention from most "Vanilla" shops. So there's a good amount of re shaping and angling that can be done, just to bring it to what I consider a play type engine.
  I do them multiple ways with more or less compression, port timing, and port volume depending on ride style.
  To go to the next step is more time spent in those ares and the intake. Also welding the rears is a must at this point as with anytime you raise compression. Head work follows suit with the riding style as does exact port heights, you can build a engine to lug more or rev out in any version, but it becomes a trade off in one direction or the other, and you have to decide where your requirements are, or let the builder make his best guess. 

Like pipster said in previous post. If you can find one and like the way it runs, see who built it and go from there.