I appreciate everybody's input and I've decided that F-402C is probably left unchanged. I'm not and engineer and certainly not a Test Pilot so we'll just leave it as is... My latest ideas have all been above "The 402C Line". I think letting the radio trays sit on 402C for support is probably easier than modifying anything. I am familiar with the use and operation of the equipment I have already, and I like that the EIS is visible as a back up if the EFIS fails.
But I'm sure that's a whole other conversation on reliability, failure rates, blah blah blah... In 7000+ hours of flying, I've never had a (or what felt like a) serious problem and I'd like to further mitigate that by somewhat planning for the unexpected.
Anyways, design/build/modify/steal/purchase some sort of battery redundancy to the Gemini ADI and EIS, and that's the minimum I'd need to get to the ground in a big problem. Or turn around and find VMC conditions.
Again, thanks for everyone's input.
p.s. It also looks like I'll be learning to build a wiring harness. My goal is to fly to SnF 2018 so I'd better hop to!