I had actually got an initial solution with your dropboxblack.bmp using GIMP to greyscale it to 16 bit.
Now a bit lost with the rest
Are you saying the ingamebriefmap.bmp bit that the map should show through is magenta and the the 469 x 463 pixel 16 bit overlay.bmp has the lines which would be on the H2S radar (the middle circle and the sweep hand)?
Does that dropboxblack still have to be used as not in your xml version?
Meanwhile I resized the maps first to your 7504 x 7376 before changing them to black and white. I assume they have to be sized back and changed to 469 x 461, but ? only after I merge the green layer do I have to change to 16 bit?
EDIT: Resizing the maps and then reducing them back made them very fuzzy!?