I was about to make that modification. I did mine with the 4 3/4" vents, and 10 3/4" holes up along the top rim, for both vent and for hanging meat off he rods with SS hooks. Mine won't run over 350.
My old style barrel, same vent setup, but with a door cut into the side for air and to reload the small fuel basket, (about 5lbs) would run 500 easy. Chicken tastes great out of the UDS, but I miss the crisp skin. Some meats, higher is better.
What was that you capped them off with? Are those magnets? I have threaded on mine, but i like the adjustability.