First off, most engine builders would likely tell you that the cylinder to piston clearance is much larger in a stock engine than what we use when we can build from scratch. Why do I want a looser fit? It would seem what you’re really looking for is less ring tension. However, by this grit method, you would achieve less resistance by loosing ring seal. Not good. Compression is king on these engines.
Speaking of compression, what kind of damage will you be doing to the valve seats as the grit is smashed into the seat by the valves resulting in serious pitting. You may be able to cut/grind the seats enough to get rid of the pitting, although you might be surprised. Again, the minimal gain you might get will be offset by the loss of valve seal = Not good.