Rick Parker You are right about the 350 drivers. Saw them at the Glen a couple of weeks ago. I think some of the reason is that a mustang cost and value to repair is about 1/3 the cost of a cobra. Mustang is cheaper in parts to maintain.
As far as what carbs these guys are running, it's been proven that webers of the 48MM size on a 289 make about 35HP and 20 pounds of torque over a single carb if setup right. Webers also need a different camshaft than a carb does. There has been HEAVY discusion about which cam design is better and makes more power. There is a guy on this forumn running 58 MM Olbergs. Motor is max preformance to the nines. HP is over 750 and this is a 20+ year old motor. The best carb and single plane manifold, carb of 1,100 cfm came up short on power in the mid range by almost 20HP. This motor is a 482 that will turn 7,800 rpms. It has a small power band from 4,800- 7,800 rpms. This motor sings once it's cleared out in the power band.
Colin can drive a GT -350, question would be the trans, that's no stock box setup. I can't see his other foot and the shift almost sound like my clutchless 5 speed.
Bottom line is we go to see them race. Every one want to win the trophy. Question is who is cheating and by how much. People that own and race these car have silly money and see these car as just that. You and me would have a different feeling about this. I am only autocrossing my car because of the amount of money, blood, sweat and hours lost of sleep put into this car. If I ever crashed this car, it wouldn't get repaired, I go fishing. Rick L. Ps Aluminum body CSX cobras are worth about 300K+ and aluminum body parts to replace about 3 times the cost of fiberglass or steel. GT-350 in good shape 75-100K. This may have something to do with driving like a wildman