the reason i posted about the allen screw was because i read your post just before i did mine for the first time. i pulled the blocks off and saw those brass screws and wondered if those were the ones you were talking about. the screws do not have heads and are recessed in the hole so they can't hold the blocks down unless they are stuck. if your scews had heads then someone may have replaced them. i looked at the cover and saw the protuberances underneath that push the blocks down and saw that the allen screws go through two of the holes in the block. so my conclusion is that they are what hold the blocks down. lucky for me my blocks just slid off. you had to do what you had to do. it's important though that the facts get stated because people do use the threads as a reference (like me).

cheers