I prototyped that setup myself because I also thought the sloped side-panels would look really cool. Here's what I found:
1. Unless you are a much smaller person than me (6'0", 220 lbs.), moving the throttles inboard and aft as you suggested will result in your left leg resting against the mixture lever inflight.
2. The throttle position ends up feeling way too far aft, IMHO, especially at low power settings. At idle, my arm was squished backward at an uncomfortable angle.
3. Rear seat passengers with big feet might conflict with the throttle quadrant, too. Depends on how you do it.
The tradeoffs were not worth for me, but they might for you. Sorry I can't help with specifics of the throttle repositioning. For me, the RV-8 is just not quite "bubba-sized" enough to have side consoles. Perhaps the RV-13, or whatever, will be wide enough...
(What I
did do is make a sloped console for the right side only. On the left, I fabricated a mini-sized sloped panel for the flap switch only. It sits just forward of the throttle/prop/mixture levers.)
Below is a photo of the right console as I was installing it a year ago. I extended it aft only far enough that it doesn't interfere with the back-seater's feet, and also leaves room for chart pouches, etc on the sidewall behind it. As far as the structure, it's basically a strong little box made of scrap pieces of angle, covered with 0.032 aluminum. It's attached to the bottom edge of the instrument panel with four nutplates/screws, and to the vertical channel cap with four more screws and nutplates. The right (outboard) edge of the console is braced underneath with angles, but it's free-floating along the fuselage -- no attach point to the skin. It holds eight or nine toggle switches and two circuit breakers, and is plenty strong for anything you'd want to mount on it:
Below is the "mini-console" on the left side. (The flap switch is not installed yet in this photo). It's made of scrap 0.032" and is attached to the top of the throttle quadrant with three screws and nutplates:
I'll post further detailed photos if anyone wants. Hope this helps. Have fun!