These disks were part of a lot I picked up today. Could they be prototype versions of Amstrad CPC games? http://www.youtube.com/watch?v=ai4XIfvlteg
Wow, a friend had an Amstrad CPC many, many years ago and I never realised that the disks weren't actually standard 3.5" floppies. I even thought that they were superior to the double density 5.25" floppies that our computer used. Interesting video.
You can build a simple cable for 3.5 drives,its a off-shelf controller chip. I had a CPC 464 with a Vortex dual 5.25 and a 6128 with missing drive where I modified a PC cable and drive.