Reworking engines is a great hobby all unto itself! You will be more successful and enjoy it more if you understand why you're doing a certain mod and the physics behind it.
I reccommend "Two Stroke Tuners Handbook" by Gordon Jennings. Probably the best Laymens one source info out there. It was slanted towards motorcycles but I've used the info on Glow Engines, Go Karts, Jetskis, Chainsaws, Snowmobiles and other 2 strokes. (same laws of physics)

If you really want the in-depth info; You can send off to S.A.E. for the Whitepapers that have been presented on high performance 2 cycle engine design. (about half of them were presented by Japanese Engineers working for Yamaha in the 60's)

What you can't buy but is important is a good log of all the pertinent info on all the two stroke engines you've modified. It should have; before and after performance, before and after port timing-compr. ratio- pipe dimensions and etc.