Removing Hasselblad QR plate

I'm trying to remove the bottom quick release plate from my Hasselblad, starting with the four small screws, but I can't seem to get any of them to move! I want to replace the 1/4" tripod socket with a 3/8" one that I purchased.

Any ideas? Are these things welded on? I'm using a precision German screwdriver here!

That could be your problem! Use a precision Swedish screwdriver instead. [and post photographs from several directions so we can see the problem]