You have certainly put a lot of thought into this. Regarding exhaust cam idler location is there any leeway there since you don't need a specific number of teeth? Maybe you could be cunning here and arrange for hunting teeth by having an extra one, and so even out wear as per Velocette practice, although timing marks only align every x numbers of rotation then.
BTW had a look at exploded diagram of X wedge engine. It appears that the bottom of camshaft chamber is higher than that of crankcase. This would leave a certain amount of oil in bottom of crankcase if the scavenge suction point is in the former, but this may be by design. I note there is a magnetic drain plug in sump as well.
