Well, here's a screenshot of a Piper Arrow III Dashboard in X-Plane:

And I try to build most of it.

As said before: I already own a Yoke and Rudder pedals, which are fine and I currently do not intent to build these from scratch. 

This might be different if I'd plan to build a full cockpit, but unfortunately there's no space for this in my apartment. So a desktop cockpit it'll be and the existing yoke with its table top screw clamps works great for this use case.

So, based on the above screenshot and the existing hardware, I came up with this layout:

So most instruments will be in their original place. Some components needed to move, since my dashboard will end on the tabletop. So, for example, I moved the starter key slightly from it's position slightly "under the tabletop" to a free space above. Same thing for the fuel tank selector, which is originally located down by the knee of the pilot, on the left wall of the cockpit, to a free space next to the starter key (I also sized it down). 

I don't have to build the throttle, prop and mixture levers, since these are part of the existing yoke assembly.  But I had to move the alternator amp and fuel pressure gauges out of the way for the yoke cutout.

There's no space for the fuel and oil pressure/temp gauges, which are originally also below the "tabletop line". I'll figure something out later...

All the switches for the lights and avionics will be more or less in their original spots. 

And I'll fill the stack of electronics above the switches (like GPS, Transponder, Autopilot etc.) dynamically as I build them. They should have all more or less the same width, which means, that I can rearrange them as needed in a large rectangular cutout (like in the real dashboard).

The backplate will be out of 5mm plywood, somehow fixed to the yoke and/or tabletop, so everything will be easily setup in a few minutes. However, the exact structural framework is yet unclear for now.