I asked the same question a few months ago: Don't expect a lot of help from many of those guys listed. The ones who are in business doing this for others are keeping their secrets pretty close to their chest, rightfully so, but most of them have brushed me off completely concerning even the general basics.

Read that thread JB linked you to, and you will get some help from some of the guys listed: Downunder, JB, and SavageJim have all been helpful to me in particular. Regarding the REAL mods to your engine (port timing, etc.) you'll have to do a bit more research, especially since that information is the real heart of the engine. JB started a thread here a while back and there's some good examples of what other manufacturers are using for port timing. It should give you an idea of what kind of parameters you should be looking for, but unfortunately it doesn't tell you much about the operating range, overall power, or fuel efficiency of the motor in question. It's worth the read though: http://www.rcuniverse.com/forum/m_7452102/tm.htm

Basically all the sleeve mods & crankshaft mods center around the fine tuning of airflow and direction and lower crankcase mixture motion. Lots of it is common sense, but much of it is nitro-specific. There are a few threads going on this - do a search and read them all for a general concensus, but from what I understand all of this stuff is best for efficiency and smoothing out the powerband, not for actually gaining power or moving the power peak upwards. THAT comes from opening up the ports, but there are so many combinations of port timing, it's going to take either lots of trial/error, an expert, or a really good computer program to tell you exactly what to do.

Unless you've taken one apart, you can't appreciate how small these parts are and how precision the work will have to be, and the scale of the tools needs to match the scale of the sleeve. For $50-100 (what many modders charge), it's a heck of a deal in my mind to send the motor to someone who knows what they're doing and has the tools to do it.