(Original Post) You said you wanted "side headers".....do you mean headers that work with the factory sidepipe mufflers. The mufflers will fit 63 to 82 C3's.
Hedman Hedder 68280 is intended for use with the factory sidepipes. Although designed for a 1969 small block (1969 was the year the sidepipes were a factory option) they will fit a ZZ4 D port angle plug head. The 69 engines had "oval" ports and straight plugs.
If you think about it, chances are a header for a straight plug SB engine will likely work on an angle plug. The angle plugs tend to move the end of the spark plugs away from the headers. I think that if a header is designed for non-AIR engines that have straight plugs, the manufacturer may not want to advertise that it will work for angle plugs (generally AIR engines) since they don't want to run afowl of engine emission laws.
I know these statements may not be of much consulation since you don't want to order a header listed for straight plugs only to find there was really some reason it won't work on angle plugs!!