What I've seen..
Not a direct answer to your question, however I do a few RV-4 "mentoring" projects and condition inspects. I built my -4 with the VAN's electric option kit. If you go that route, you need your center floor panels opened up and it will provide you with all the new weldments and a couple brackets that need installed. The actuator will lay flat under the floor, the existing flap handle will be removed and additional crosstube nylon blocks are installed. If you choose the other installations I have seen, the actuator is most often mounted vertically to the R/H fuselage stiffener below the roll bar, and connected directly to the existing flap actuator weldment, with the manual flap handle removed and sometimes, the mount tab for it cut off. I have seen more of the homebrew mounted actuators than the VAN's factory set-up, likely because it may be cheaper and no need to add the bracketry under the floor. Both work well, and you should be able to search threads and find some pictures. I put my flap switches on my MAC stick grip along with electric trim, so no need to take hands off throttle and stick for pattern/go-around work.