But Mark, you're a lot scarier in person than you are on a web forum.

Besides, the airplane is pretty far out of trim; alternating making the airframe better with making the motor better might get me to the Tune Up in better shape than concentrating on one or the other for too long.

me scarey,
sheesh,,

Reading your description again I had this following thought. It is typical and desirable in many ways for a UC plane to lean out in overheads. Overhead, gravity is pulling the fuel away from the pickup creating a leaner mixture. Desirable since more power is needed to keep the plane out there on the lines when airplane speed alone is counteracting the pull of gravity. In level flight, the weight of the plane is supported by wing lift. As we get further and further above level flight, airplane speed and the centrifugal force created by an airplane flying on a tether, keeps the lines taught, while overcoming gravity. Most engines noticeably lean out in the overhead maneuvers. In moderation it is considered an element of a good stunt run. If you think the airplane is speeding up too much add a head gasket,  and/or go to a smaller venturi. I would use a smaller prop. The 10.5x4.5. sport APC works for me.  A larger prop might complicate finding a happy needle setting, a setting where the engine pulls well throughout the pattern, without over speeding. It is possible that your tank is too fat, hard to tell without seeing the tank in person. I notice that the sides are belled. A flatter tank might reduce the transition changes as fuel is consumed (and fuel head is reduced) during the flight. I have had chicken hopper tanks work well on stunt profiles when space is an issue. The hopper seems to reduce the effects of fuel head change. Also, if cutting out is a problem, a chicken hopper might provide a better and more consistent feed. I usually run these and other tanks on muffler pressure and uniflo. On occasion vibrations issues, common on profiles, create problems, uniflo bubbling can exacerbate vibration induced foaming. Running without uniflo has helped in cases like this. If you suspect fuel foaming might be part of the problem, try running pressure to the overflow and cap the uniflo. Or cap the uniflo and vent with the overflow.

What he said.  
Best description, in my opinion, of what goes on at the top/ overhead on this post. Like all say, many more knowledgeable and persistent folks have tried different alternatives. It is not by chance that they consistently come up with the same conclusions or set ups. I could have saved a lot of pain and frustration if S.H was around 30 yrs. ago.
Then, the only way to obtain valuable knowledge was to attend as many high end competitions as one could and ask many questions. Now, we have THIS PLACE. Wished I was 30 yrs younger...

Rafael