Drops the cylinder down for a bit more squish and compression but doesn't do anything for rpm.
Not much of a performance gain, maybe just detonation. Not recommended.
Cut gaskets out of paper or cardboard if you want to try it, no waiting for shipping.
Better answer is to stack gaskets up for a better exhaust port position.
Get the piston flush with the top of the cylinder and get a head rechambered flush.
This works.