Jim,
This isn't about keeping the wing straight, but it's another aspect of the Shark 402 worth considering early in the build. The controls on mine are extremely sensitive. Even with a 2 oz shaft weight on the Brodak .25, and about 25 degrees up and 25 down elevator deflection, it takes a narrower handle spacing than I like to hold it steady in level flight. If there is a next one (which there may be, because it flies great, turns tight without stalling, and looks terrific), I would build the nose about an inch longer, move the hinge line back about an inch (more stabilizer, less elevator, same overall horizontal tail area), and use a 4" bellcrank to allow a wider handle spacing for more positive control feel without excessive control sensitivity. Aside from that, the S-402 is a real sleeper among medium-size flapless stunters worthy of more attention that it has received, IMHO.
Kim Mortimore