I want to get headers for my truck. I also plan to get vortec heads next month.
What is an angled plug?
I can't answer your question about the size of header primary tubes, but I can answer about what angled plug heads are.
Look at how your spark plugs stick out of the heads. On most small block chevy heads, the spark plugs stick straight out. On angled plug heads, the 1st and 2nd spark plugs are angled towards each other and the 3rd and 4th plugs are angled toward each other. This was done to supposedly give the spark plug a better angle inside the combustion chamber to ignite the air fuel mixture.