Darius,
I couldn't find the original post of that image, so I reloaded it.
Here is the image of USS JOHN W. WEEKS (DD-701) dated 1 March 1945 showing her Radar Countermeasures (RCM) "stub" mainmast. Not many SUMNER's had these RCM Stub Masts installed. I don't have a complete list of which SUMNERS did, I have seen several images, many are distant views where the ID of the destroyer can't be determined. There were at least two versions of the RCM Stub Mast, the one that was installed somewhere on the West Coast and there was a version that PHNY installed during the period between when the initial RCM suite was no longer authorized to be installed and when the new RCM suite was available. Once the new equipment (with DBM, etc) was available, the USN installed the DBM antennas on the aft stack of SUMNER and GEARING class units and the rest of the antennas elsewhere on or near the foremast.
The original RCM mast design for the SUMNER and BENSON-GLEAVES class units (only one unit I know of actually had it installed on a GLEAVES class destroyer), had a single crossbar at the top in a "T-shape" with the APR antennas on the ends. This was similar to the mast installed on FLETCHERS late in 1944. The PHNY version was also a "T-shape" with APR antennas on the ends, but had two supports from the crossbar down to the stub mast. Also, PHNY installed a single early DBM antenna atop the stub mast.
I don't know the exact location where the RCM Stub Mast was located. but hopefully the three images I have posted will narrow down the location some. Particularly the near broadside view of USS CHARLES S. SPERRY (DD-697). It looks to me to have been installed alongside the portside Mk 51 director of the quad 40-mm mount and aft of the emergency con station on the centerline.