Steady on with recommendations to lean out. There was a lean burn kit a while ago and caused many problems.
A key problem here is not the max or min EGT but the spread.
Those with full monitoring will often see 100 deg C difference in EGT between cylinders. It also changes in different modes of flight
All issues of rich or lean go out the window because you can have BOTH in the one engine at one time. I have seen some where they are fairly even.
Ive too done lots of playing with needles/jets etc and ended up as best I can get. Never over 710 degC, cruising under 690 BUT have sometimes one under 600 at the same time
With CHT, can get them near 120 most of the time, fitting under cylinder deflectors (the gull wings which used be installed on top) certainly stabilised temps and made them easier to manage.
Jabiru USA have a good PDF on air duct "tuning". Fiddly and time consuming but worth it.
Theres some evidence that this variation in fuel distribution is done upstream of carb. work continuing. Not much there so not easy to fix. It has been a thorn for years in carb auto engines too and they are water cooled! strong reason they adapted quickly to port EFI.
Many of the current throughbolt and valve issues are linked to hydraulic lifter introduction, sorry Rutan it wasnt a good move. Keep in mind you still have to open rocker covers anyway to tension headbolts.