It can be done, but you are far better off buying an engine that is already timed to fit your requirements, be it C/L stunt, pylon racing, sport R/C, combat, or whatever. The crank timing works with the bypass, boost, and exhaust port timing. Then there is compression ratio, plug heat range, ntro %, and exhaust tuning to consider. They all work together and the effects of one change do overlap others, making it even more confusing.
You can experiment if you want to, just don't expect to improve on the designs already out there, especially if you are just trying this for the first time.