Yes, that area in red needs to be cut out. In the original literature (which I have not seen, just had been told to me) that area may or may not have to be cut out. I do it on every DC k-member that I build just because that's the easiest time to cut it.
Also, that IS an original DC part and not homemade (there are telltale signs). The mounts only fit one way (the one with the long bolt is the driver side).
