I have a third stoplight and base that I was told came out of a 126 that I want to put in my 84 126. Can someone tell me if it mounts on top of the rear shelf fibre board, or do I cut the board away and drill through the steel shelf below? The curvature of the base does not fit the curvature of the fibre board and I am concerned that it may not be for a 126. Also, when mounted, does the lower edge of the light housing come right to the bottom of the rear window? Thanks in advance for any info.