There are many things that can be done to RC airplane engines to gain more power. Things like you mentioned. The thing to remember is racing engines for motorcycles, boats, and cars for that matter are modified for top end power. If you were building a gas engine for somthing like a pylon type plane this would be fine. But for regular flying like most of us do, that kind of engine is impractical. We need an engine that runs well in all of the rpm and throttle range, and not just flat out wide open. Many hopped up engines make great power at top end, but do not do well at much more than full throttle. Also engines like racing go carts and such make thier top HP at well above 10,000 rpm. That is an unusable power band for us. We need low end torq. As an example. Take a .15 car engine for a remote control car. It puts out 1hp + in some cases, but will not turn a prop for crap because it hits it top HP at almost 30,000 rpm.
You can change port timing, compression, and other things as well. As I am sure you know, port timing changes can do a lot of good, or a lot of harm. It is a fine line between too much and just right.

Just my opinion. I have built over 500 RC airplane engines so far and have learned the wrong way to do things on them for sure I am still learning though.