Engine rules should be made or advised by people who have knwowledge of engines.

The 5 port rule with a 7mm insert is I believe mainly a cost rerduction so no high end 9 port engines can be bought. But nothing is sayd about the internal timings and modifications. So you have a cheap 5 port engine and then you buy a set of ceramic bearings and let it be modified by someone making it a total price of a 9 port engine.....