Changing the timing is not something you want to do unless you plan on doing alot of trial and error on different motors/ sleeves and cranks. That is usually left to the professional engine modders. Basically you bore or grind out the intake and or exhaust ports in the sleeve and crank to achieve optimal timing. I don't know much about what timing is optimal... hard info to find. Most people that know what timing is best won't tell you what it is...

I'd just stick with the fangs in the sleeve and crank then slam some putty in it, bevel the crank intake and call it good if I were you.