Unsolved Making a new body configuration

Hello,
I am looking into editing a certain car's body, but I don't know how to make it a configuration in the parts selector. The new body wont need a new Jbeam, as it will have the same dimensions as the original. any help would be appreciated, thanks

(if you need more info than this then say)

 

Well, it depends on what car, what you want to do to it, if I were to help, I need more information.

 

I want to make a 2-door version of @NinetyNine! ’s ETK S-Series for private use (If I ever want to upload it, then I will ask his permission)

 

Shorter wheelbase or regular wheelbase with an extended door?

 

Regular with extended door.

 

I didn't make the S Series that was NinetyNine

 

Oops, I’ll edit it
When I was looking at the S-Series I got a notification that you quoted my post in the WBIMP thread, and then made this thread and muddled up the names. My bad

Also, do you have any idea how to do what I’m trying to do? I know you’ve made lots of great mods in the past