My buddy just installed a freshly rebuilt 70 440 HP in his charger. 6 pack, MSD ignition, headers. It runs well. But #8 is having an issue. The top of the #8 header tube is getting cherry red. So hot it melted the spark plug boot. #6 is plenty hot too but not quite as bad. What could be happening here? Thanks for the thoughts.

Likely a vacuum leak at the intake at the #8 intake port. Hot = lean.

x3

Could be a gasket/ port sealing issue, or possibly a crack in the intake, but something appears to be leaning out that cyl. and possibly #6 as well.

You dont say how hot 6 is but first thing I would check is the vacuum fitting connection at the back of the manifold.
Check the hose for cracks and see if it is attached on the other end.
That fitting leads right in to the #8 port entry.

use a temp gun,to see how hot,but sounds like a vaccum leak

Thanks guys for the suggestions. Much appreciated.

keep us posted on the fix