I ended up changing up my LED 3rd brake light setup, and have this plate leftover from the previous version. It's drilled out for a Rigid A-series style light in the center with 2" mounting hole spacing. The outer 2 spots are drilled out with 1.75" spacing. I was using the old style Rigid UTV dome lights, but found that those had issues with rust forming inside the lights. I'm sure you could find a different style light to use instead. The plate is powder coated semi-gloss black.
To complete the light, you'll need to crack open your OEM third brake light housing, and remove the lens. Once you've bolted your lights to this plate, you bolt the plate and the OEM housing to your vehicle and you are good to go. Here's a pic of it when it was on my rig:
Asking price is $25 and I'll ship it for free.