This is my first manual f-body, and I dunno how long a short throw shifter would be, if the previous owner even replaced the shifter in this car.

How can I tell if it's stock or not, and if it's not, which one it is?

 

I just changed my shifter today. I would just take the center console out, and take the rubber boot off and take a look. It won't take more than 15 minutes or so.

Here's a guide that might help:
http://www.projecttransam.com/projects15.asp

Dan

 

If you take the shift boot off, you can see if it still had the rubber isolator on the handle. If it doesn't then it's aftermarket.

 

not nesesarily mine still has the isolator and its a B&M so if its still there then take it off and then you can tell by the markings on the shifter plate