Its pretty easy to check if its timing. With the engine running turn the distributor. If it runs better, headers stop glowing theres your sign. Then you can worry about the other issues. Seen it MANY times and it has always been a timing issue. You won't hurt the engine if the ignition timing get advanced to 40-or 50 degrees at idle. There is no load on the engine at idle. Id be willing to bet its off 14-20 degrees from where you think it is. But if you advance it and it gets better you have an answer, that costs nothing and takes minutes to try.

You seem to have another issue being a vacuum leak. Gonna have to be a HUGE leak to turn 8 headers red, not just a random cylinder or two. Think about it...The headers being red is 99% of the time from fuel being burned in the header rather than the chamber, they dont get that hot from a LACK of fuel