In 1974 the classes were different. There were no gasoline classes for Streamliners, Lakesters, Comp Coupe, and Modified roadsters......They were real race cars and real race cars ran on fuel (or anything they wanted)
The addition of a supercharger of any kind bumped you 2 classes, so an "E" with a blower ran with a "C" naturally aspirated...Get it?
Now that you are confused the gas coupe had 2 separate classes supercharged and nonsupercharged: Thus C and SC . It was the only one that way, which is really what we have today.
Get this there was no penality in Streamliner for a blower...it was just inches...........Life was great, every one knew what a step pan was and the rulebook was real, real thin...Oh yeah my first year.......................JD