Joe welcome to the forum, once your membership is approved, I will move this to the New Collector area of the forum.
yes, a stock would make it into a carbine. It is ONLY legal to use a stock on certain models, otherwise you are breaking the law.
Also, you will have to post lots of pictures, for us to help you better.
You can search through the forum and find carbine pictures.
It is hard for us to help without you giving us information, pictures, stock dimensions, etc.
Ed