All those handbooks are written arround larger motors with an electric ignition. And yes, the basics of ports, exhaust, intake, bore/stroke, crankcase volume etc can and may be directly transferred to our engines.

But our engines have a self combustion concept where some factors have influence on the ignition timing and the shifting of it. Those are not hard to understand but very important to understand our engines and why some changes are not doing as expected or doing half as expected.

Because it is a smaller engine with low placed ports a 0.1mm could give arround 2 degrees extra timing. I would make a 0.1 and a 0.2mm shim so you can experiment 3 positions.