I know that your headers are stainless steel, which alloy? 321 is what it should be. Radiant heat, powerful stuff, it is driven by differential temperature and the distance between the hot part and any other parts, as I remember if you double the distance you will reduce the radiant heat transfer by a factor of 8, so you need lots of good reflective shielding and ceramic based insulation and lots of distance between parts, like fuel lines and the heat source. Good air flow over the affected area helps, as it cools the affected parts by convection, it has no effect on the radiant heat transfer.
Sorry to hear you windowed the engine.
Rex