How can I tell which radiator I have? Do I simply measure the thickness?

 

Yep, that's all you do. It is either about an inch (1.02) or about an inch and a half (1.42).

 

Open your hood, stand on the driver's side corner, look at the sticker on the upper driver's side tank (if it's still there it includes a part number for reference), then look at the center section behind the side tank there (there is a nice window to look there just under the plastic cover). You're looking for the thickness of the core or center section; it's silver/aluminum in color.