If you use an actual 1680 case from Phong, NDT or Yuki, a 5512 dial is going to be too small. The only exception would be the MBW '1680' case which is actually just a renumbered 5513 case (for example, a genuine 1680 dial in an MBW '1680 case won't fit as the dial will be too big).
jsuperman- I think a MBW case is going to be the best best for your project. Relatively low cost and definitely one of the better quality cases out there. The bezel rotation/play will vary among watches; even one MBW to another. This is adjusted by giving the bezel washer a slight bend.
Hope this helps.
Cheers,
//ubi