https://www.instagram.com/p/BRwgf8bgGWV/
Our 1st & only view of the inside of the interstage. It probably would have cost a few thou from the BFR budget to put a roof on it or strip out all the guts, so Musk said forget it. They did strip out the pushrod that ejects the 2nd stage & hastily strung an extension cord to a warning light. The extension cord had a little left over. 2 wires in mid air appear to be additions. They could be a radio antenna used by someone else. What are the chances of retired Falcon 9's being sold as cell phone towers?
You can see everything mounted directly on the convex top of the LOX tank. Not content with plain old rods, they used horn shaped rods. It must be the most weight optimized way to transfer torque from a narrow diameter to a wide diameter.
There's a triangular enclosure which could only be a triple redundant brain box, where the 3 computers are mounted symmetrically. All the software flying the 1st stage & the IMU are probably in that box, all calibrated for its orientation on the LOX tank. We also see what could only be the nitrogen thruster tank & the pesky hydraulic fluid tank. Surprising such a small tank is all the nitrogen it takes to fly it back. There's no effort to balance it by mounting the tanks symmetrically.
The torque rods are already looking a bit rusted. The guy obviously doesn't know a 4k copy of the video is stored on the quad copter, but barely knows enough to hit send on an instagram app to upload low res telemetry.