Headers

I'm no professional, so your results may vary.
Don't forget timing; at 2000/2200 the engine will want plenty of timing. I'd wager that retarded timing, allowing the fuel to continue burning in the headers, is the number one cause of header bluing. The engine is gonna want in the range of 40* to 50*, or more degrees timing, and most engines will never get this much,probably because newbie's just don't know this, and many/most wouldn't know how to get it.
So when I break in an engine, as soon as it lights off and gets up to rpm, I just tug on the D until the rpm peaks. Then go about the other engine-saving business. This ensures that when the exhaust leaves the cylinder, it is about as cool as it will ever be.... at that rpm. I set the timing later.
With proper timing, at no load 2000/2200; the PV is locked up tight, the carb should be running only or mostly on the transfers, and the engine shouldn't care one whit about the size of the MJs. ............. But the engine will want a ton of timing.
I haven't broke in that many engines; but using the pull-it-to-max-the-rpm timing method, I've never had a color change, even with nickle-plateds.
I'm no professional, so your results may vary.

For skeptics out there, especially you no-Vcan guys,just go out and set your engine to 2000/2200, measure your pipes with an IR gun; then pull in the timing as above, reset the rpm, and retest the temps. Then put a timing light on her and see what she's getting. Finally stick your fingers over the boosters and see what happens to the rpm.