All things being said, always measure. However, kids have been building these things for years. Problem is they grow up to be old men. We have honed the cylinders to remove the top ridge for years and STOCK rebuilt the engine. Sounds like that is about what you are doing. Crank excepted. Build a racer and you dam well better mic everything. Once you build one, you can not wait until the second one. As much as measuring is important, remember that a VERY clean area is equally important in a good build. Time is not a real factor. However once you clean things, you don't want to wait to long for dust and things to get into your project. Let us know when the hook is set and how your project turns out. No Fear.