First and foremost you NEED to get a rulebook as it nautrally tells you what you can and cannot do.
Per the SCTA rules, an American El Camino is considered a car and NOT a truck and can only run in the car classes.
I am assuming that your El Camino would be considered the same but you would need to email the SCTA Car Tech Chair for verification.
In addition to what Steve posted, there are other classes you could run as well and you will find them and records listed in the rulebook.
Look through the book when you get down to Mikey's.
As usual, hope this helps.
Gregg