Using a Claw on a bike with an integral hangar may work, Campagnolo parts will not, the claw offsets. The claw will have to have the bolt hole for mounting the attachment at the same point, as the mounting bolt extends a bit beyond the claw, and I don't think the threaded bolt will pass through the Simplex hole.
In this case I would search out the recommended Simplex parts, or tap and file as another post has shown.
If its a PX, then I would not, a
PR, well its not that a big deal.
Forgot the original poster said UE, Simplex or tap and file.