i just put together a 400 small block, flat top pistons, stock heads, mild cam 280 advertised duration, 465 lift. has a performer manifold and 750 demon carb. the cam is in 4 degrees advanced. after i start it and start revving it up to about 3 grand some of the header tubes are getting red, mainly 1,7,6,8. 2 and 4 do not get hot at all. the timing is about 17 degrees btdc. it has no vacuum advance. any suggestions?

Make the timing about 38°-40° at 3000 rpm then hook up the vacuum advance.

I've seen this caused by too much retard on the timing. I'd bump the timing to about 22 and see if you get any detonation.

i just got done switching the cam to straight up and ran about 20 degrees initial timing. now when i hold it about 4grand they slowly start glowing in the dark. it seem if i keep hitting the throttle it goes away. i think maybe a carb problem? should headers glow in the dark at all?

Its too lean, whether its mixture or vacuum leak. 17* btdc initial is plenty of timing

What balancer are you using? Does it match the timing marks? Some of the 400s may have come with a balancer that times behind the water pump instead of off to the side. If you get these parts mismatched you'll think you're timing is advanced when its really retarded.