I can tell you have had a lot of "seat time" learning the software.
BTW, I have never seen a 4-bolt main 6 cylinder. That may help cure some of the destructive harmonics inherent in an engine config. with long cranks.(May not be an issue in miniature.)
I noticed the siamesed cylinders too. Generally, higher performance engines have the coolant water go completely around the cylinder, where the cylinders touch you got hotter temps with no cooling water. (distorted cylinders)(some cylinders have 2 flats and some have 1 flat. Symmetry most of the time, is better.)
You may not need a ground electrode with a 3mm plug. Maybe it will jump the gap between center electrode and threaded body!
Looks like a racing engine with the equal length intake runners, very short exhaust ports, and small chambers.
Great job, Alexandre. :bow: