Radio: On its side on the opposite side to the engine controls. I built a box out of marine ply to protect it from passing knee caps (well, OK, vice versa to be honest!). I am in the middle of building an "instrument pod" to fit to the top of my console, although you have the small problem of a lack of flat space to bolt anything to.
Regarding the plotter, havre you bought it yet? If not, you could buy a combi and piossibly fit where the switches are? Not ideal, I agree, but at least fitted. As Pol says, screens are duifficult to read in a small bouncing boat! (I used a Garmin 12, and had it on "street mode" as it gavce a nice "glance at-able" display versus some tiny arrow on a pixelated map).
A mapping handheld may be another solution, and may be particularly good if you are serious a bout changing the boat. It will either be another "toy" to entice a buyer, or you keep it and have an independent battery powered GPS should your electrics or plotter fail on the new boat.
It's also amazing how a decent set of waypoints can help nav on a non mapping handheld, but that;s probably another discussion.