Sorry for the radio silence, real life has been calling.

I picked the X,Y zero to be the front and center of the pocket. You can locate that off the mag well and/or the bolt catch slot with dimensions from a drawing.

I've labeled each endpoint of every segment along the toolpath. I propose to start at point A as it will not touch the final surface at that position so any funny marks from plunges or dwells will not affect the final finish.

The next step is to find the coordinates of all of these labeled points. Anyone care to give it a shot? It is just basic addition and subtraction using the given dimensions...

Edit: BTW, I am using CAD to make all this but pen and paper is equally effective. I am using CAD as it is a lot easier to make a legible copy ready for upload.