Flow work is not that hard to do, changing the timing is a complete no no unless you really know what your doing, or starters you need to know how to measure the timing accurately & from there it gets much more complicated.
To answer the Question, YES Time to port, a RTR engine is the best place to start.
I'll give you a HUGE hint. The By-pass ports (bottom one on the side) you want to make your angles the opposite direction of the rest. you want the flow to go from the inside of the sleeve out and upwards like in this pic
That's ERCM basic porting before any of the crazy stuff gets done, this is a Highly Respected Engine Modders work, not something you will be able to see everyday.
For the rest of the work follow the guide TRXaddict posted, its actually very good basic flow work.