That is an American pen, made around 32-33. It has the same shape as the last of the Swan Eternals made in 32, but these appear to have been the first of the post-Eternal pens. Of particular note is the tapering at the cap and the barrel, and it maintains the "step" clip (these are the last of the American Swans to have it).
These have been incredibly difficult pens for me to find, particularly the 6 size. Great find.
Please join the Mabie Todd Swan project where I am trying to sort out the undocumented mess that is American Mabie Todd's from the 1930's. The last pens that MT seemed to advertise were the "Eternal" pens, and then the company put out a wide range of different styles, shapes, sizes and filling systems before eventually closing up shop. I invite you to post your pictures of your American pens
The Mabie Todd Swan Project