I think he wants to drive the SC in championships : you need to set the dedicated classe tag
Open the CAR file of the car you usually drive in a championship, go to last line at classes="..." and copy-paste the championship tag in your SC CAR file in classes line
By example, If your championship tag is 2003 then open SC CAR file and add this tag with notepad :
Classes="full, 2003, ..."
OK - thx for hints. So I let the origin SC untouched and just add the mod and it should work!? I had read in the past that the SC has to be named "maserati"... in the files so the game can read it. However I'm gonna try and report back!