Regarding the OV10 ejection seats. An old friend of mine at one time was the highest time OV10 pilot in the world, with over 4,400 hours in the airplane, 2,500 over Vietnam. He loved its ejection seats, and had a wingman punch out inverted at 300 AGL and walk away from it in 1973. I'm sure it would be easy to adapt more modern seats to it, but it's still an unpressurized airplane limiting its range and suitably as a COIN airplane compared to more modern designs.
Even with a combination of drop tanks, Hellfires, Zuni rockets, and/or 250 pound bombs on it, the A29 is a pretty good airplane, and unlike the T-6, carries a pair of M2, .50 guns internally. Both of them can sit up at FL210-260 for a long time with less pilot fatigue than the OV10.
They cost about $2,500 an hour to operate.