Nick, I'm reallllly hoping you didn't remove 402B as it's the vertical bulkheads on the fuse sides. In your picture, your 402B's (left and right) appear intact. F-402C is the horizontal member to provide rigidity to the canoe as the panel with all of the holes cut in it for instruments can't guarantee the same strength for the fuse.
I'm on the other side of the fence... I would caution against modifying 402C.
Have you ever sat in the last row of a long airliner and watched the overhead bins in turbulent air? The whole fuse flex's and moves quite a bit. I know RV's are much different airplanes, but some of that force is still happening continuously on your airplane. Every roll, every bank, every bump in the air. There's a lot of things trying to twist your fuselage.
In a perfect world, you might not ever need the extra strength. I'm sure most people who've modified it have airplanes that are just fine. And as with most things in the homebuilt world, there's nothing stopping you.
I look at it like drilling holes through the fuse bulkheads for cables and wire pass throughs, the fewer holes in the original structure, the better. I've seen a few crashed RV-4 fuselages, weather in person or pictures, and they've all crumpled or failed at the extra holes or where something was modified from the plans. My 402C is intact because you just never know what forces its there to withstand. I don't believe the instrument panel (with holes in it) to be structural. I'm just a dumb airline guy, not an engineer, but it's only held in with two bolts... I know once the forward turtle deck (avionics cover is installed) there is A LOT more rigidity added to the structure which a panel does play a major part in. But again, airline guy over here, not a structural engineer.
Attached is a picture of my panel. F-402C intact. The bottom of the panel is raised 1" for knee room and the Garmin GTX327 transponder on the lower left is sitting on the 402C. The rack is mounted to the top of F-402C. Still, plenty of panel space for an IFR panel. Just my $.02.