Ihave been doing port work on my engines both glow and automotive for 20 years or more. Just think to yourself that flow doesnt like sharp edges or sharp corners and rough surfaces. Mirror polished is a waste of time , just smooth. And dont remove a bunch of material thus increasing the volume inside the case.
Not all engines are going to give up a bunch of power but if it wasnt optimum from the factory you can find quite a bit.
A Jett engine may not respond like my Thunder Tiger to the same mods because the Jett is already a Hot Rod. But we are not talking about that , we are going to find some cheap horsepower from an inexpensive engine without spending any cash.