I did manage to get a set of E Cams on ebay. My suspicions were correct in that the C cams can be modified to fit in an E cam machine. The shaft size on the machines is whats different so drilling out a C cam will then fit an E cam machine. But keep in mind that not all stiches will work because not all machines have the ability to do all disc designs. My 1503 doesnt have the capability to do patterns that require reversing via disc. (Did I explain that right?)
The Disc measures .9845 (inside diameter)
The shaft measures .9840 (inside diameter)
A 25mm drill bit is .9843 (outside diameter)
A 63/64" drill bit is .9844 (outside diameter)