When I built the first FT Simple Scout with the balsa diagonals, I didn’t make slots for the pushrods. The foam board fuse has slots but i thought that I could somehow maneuver the pushrods through all the open spaces between the balsa sticks. I couldn’t find a way to do it. So instead i decided to mount the servos on the outside of the fuselage and use carbon fiber tubes as pushrods.
Make some short Z-bends for each end of the carbon fiber pushrods. Make sure the piano wire is a snug fit in the tubes. Then I used thick CA to fix the Z-bends into the tubes.
If you use a Dremel tool or power saw to cut the tubes you are liable to put some cf dust in the air. You don’t want to inhale that so I use a miter box and hand saw for minimum dust.