I have quite a bit of experience running .12-.15 size Mod car engine's, and these mods do work if you know what you are doing. All you have to do, is to look inside any of the purchased Mod Car engines that come with these mods to begin with to realize it really does work.
Another simple trick is to bevel the bottom of the liner, since most of the stock engines I have had apart do not have much of a Bevel.
I have never tried Modding plane engines with any of the extreme Mods, because I do not think they spin high enough rpm to make it pay off where the .12-.15 size Mod engines are easily spinning upward of 35,000 and more rpm.