Carb or efi, ignition timing principles are the same. Excessive ignition retard that burns late enough to push much of the combustion out the exhaust, causes an afterfire. But excessive advance (coupled with lean conditions) would go through the intake, and backfire. No doubt, there is more than one situation that can cause glowing exhaust at idle. But ignition retard is a very common one.
The cold-start misfire points to a lean condition. Obviously fuel needs to be adjusted first, but keep in mind engines (especially with modified valve events) tend to idle in their happy zone at all different afr's. One of my mill's is very happy at 19+:1 at idle. Granted, unless you can read inside the chamber, trying to obtain afr's at idle with an unrestricted exhaust and lots of overlap doesn't produce very accurate readings.
Given the information provided, I would start by verifying the cam install, and record the opening/closing and checking it against the specs. Then, the fuel mixture and on to ignition timing. Call the cam manufacture and obtain their recommendations for your combination. Mechanical, fuel, timing... always in this order. Then drive and watch afr's and knock.
If the header is still glowing, I would check the primaries with a IR thermometer, it could be that the wall thickness is thin enough to put off a glow in dark conditions.
just kidding... i'm done