Shortening West Coast Mirror Arms

I recently got hold of a set of stainless steel west coast mirrors for my econoline pickup project. I need to shorten one leg of each of the mounts and I have heard there is a tool for reshaping the end of the tube when this needs to be done.

does any one know of such a tool and would it be possible to post a picture of it.

thanks

Something like a deburring tool?
http://www.royalprod.com/product.cfm?catID=7

Or a reamer?
http://www.grainger.com/Grainger/plumbing-tools/hand-tools/ecatalog/N-979Z1z0du7h

Or are you thinking something else?