I was inspired by ojait's inlay answer and combined it with the TapCon recommendation.
I got four pieces of 2" x 1" x 10" green-treated plywood and glued two pairs together using silicone.
I placed the mount against the wall and outlined the screw hole locations, then laid each plywood inlay over four end screwhole outlines and outlined the plywood. Using a drywall saw, I cut out each side. I found an electrical surprise behind one hole. What are the chances?
I wrapped the mildly cut outer shell of the wires in electrical tape just in case, then pushed the wires aside and placed the plywood inlays. They stuck out more than the drywall, but there isn't much I can do about that. I put the mount over the plywood and again outlined the screw openings. I labeled the plywood: front right, front left, then drilled the holes using a wood drill. I made sure to bite into the backing concrete. I removed the plywood, then used the appropriate TapCon drill head to drill through the concrete at least an inch deep in the spots marked by the wood drill.
In the center, even though there was a gap, I used a self-drilling screw mount. I placed the mount over the holes and used 2 1/2" blue TapCon concrete screws with washers to hold the mount to the plywood, through into the concrete. I used the appropriate screw for the middle piece, but it was not necessary. Eight (six for the experiment) washered TapCon screws through plywood into concrete was enough to hold my 270lb body weight. Then I spackled over the edges where the plywood met the wall. Game room almost complete!