I do not have a heat stove on my truck, and at 22 degrees, or there abouts, temp my carb freezes! Ice will actually form on it. I woukd have to find a place to pull over before it died and let the engine bay heat back up and thaw it out. I don't think it would happen if I had some sort if heat to the carb. That was when I lived in Alaska, hasn't happened since I moved to Arkansas though.

I have long tubes on my 351w, and they hang pretty low, but was still able to get my pipes up over the CM. They may hang lower on a 460 though.

And I am of the opinion that headers don't do much with MPG increases, but do give a "little" seat of the pants increase.

 

Headers do increase power, it's a proven fact. You can run them, I just like to advertise the drawbacks that are never brought up by the people who sell them. You have to balance power increases with functionality. If you have a street machine, the lower hanging collectors may not be a problem. But when I hung one up on a stump in the woods when I was cutting firewood, I realized they are not practical for a off-road vehicle.

Same with the heat to the carb. Yes, a cooler air is denser air, and denser air along with some added fuel means more power. That's a common fact also. But that's race theory on a engine driven at the track, usually wide open, sometimes fixed timing, and they don't mind fiddling with the engine and letting it warm up for 20 minutes before using it. They don't usually run their engines in 40 degree weather either. The bottom line is an engine will not burn liquid fuel, it has to be atomized into a mist. Atomized fuel from the carb will turn back into a liquid when it hits a cold intake manifold. They run heat through a passage under the carb, most racers block this passage. They also heat the air with a stove we were talking about that goes up to the air cleaner snorkle. This helps heat the carb and the intake as well, and combats the problem of the venturi freezing up. Ever spray a aerosol can for a long time and the can gets cold and the nozzle gets frost on it? The same thing can happen in the carb as the velocity increases through the venturi and the fuel evaporates into a mist.

 

460 trucks were ALL over 8500 GVWR, no cats, no unleaded fuel stickers.
I am running essentially what you are planning, other than the exit, my exhaust ends at the magnaflow, muffler is the smallest case with built in crossover.
I have ran for years without a choke stove with no icing issues, however my climate is colder and drier than yours in the winter.

As for how it sounds, you tell me.