Thank you for your inquiry regarding the MB516SP-B and the issue you have. While we try to design our products to fit in as many cases as possible and following the standards of 5.25" size bays, unfortunately there would be some cases that would have a few odd case designs that would prevent the usage of our products. For your case, you would have to modify the metal flanges in the 5.25" bay, either by sanding, bending or removing them, as those parts is preventing the insertion of our products.
Please follow up with us if you manage to get our product in your system. We would like to know how and what you did to fit our product and it would be helpful to others who might have the same issue as you.