I'll admit to being old. However, I think I know a little about engines. My articles were written for beginners. The really essential tool for modifying engines is a dyno. I've encouraged that for years. The other essential tool is research into the latest two stroke thinking. Again, I belong to forums along with the world's leading two stroke developers.
Our industrial engines are crude compared to modern thinking. They were designed to be inexpensive to mass produce. They make a great spec propulsion system for models and have largely replaced nitro engines because of their durability, low initial and operating cost, and reasonable power. There are much more modern designs available, but the low cost Zenoah still dominates.
I have a Monarch 10ee lathe and a Supermax mill. with tooling and a chest of machinist's tools They have machined a lot of engine parts. I've also made tooling to help modify engines. Mark Anderson has all my engine tooling and completed an excellent dyno from my parts. Neither of us sell anything to the hobby. We only hope to improve the experience for others with similar interests.
PS I designed and built my first engine in high school. It won two industrial arts prizes.