For an engine as old as yours, with as much run time, that is a hell of a lot less carbon than mine! Since you have also changed yours to a negative pressure crankcase, have you considered changing to a higher ratio? I have seen some people (cant remember who) that are running 30:1, so thats where I am going to start. I wanted to try and get the Stihl HP Ultra, but there isnt anyone who stocks it in the UAE, so will have to go with the plain old HP.
My parts should be arriving soon, so hopefully I can get this crate running again soon, and will probably fly it on a 3D plane, for the same reasons you are....if it quits, I can get it back....
I really dont know how long parts for the FG60 are going to be available, but I think this engine will be disco'd in the not too distant future. Just getting valves was a problem. If they are wearing like yours and mine, then putting new valves in, would most likely need new cylinders as well, as the seats will be worn too. Basically a new engine...
I am going to get a UMS 90cc 7-cyl radial next. It is the same diameter as the FG60, with possibly a bit more power. The best thing about the UMS, is that the cylinder head is seperate from the cylinder, so maintenance is possible on each cylinder without having to remove back plates etc, you can even replace/maintain in the plane.
Better or worse than the Saito, time will tell..