Just answered my own question with a bit of research:
Two more B-47Es were converted to EB-47Es in the mid-1960s for US Navy service, on indefinite loan from the USAF. They were very much unlike the USAF EB-47Es, with some of their ECM gear fitted into pods carried on the external fuel tank pylons. They were used for tests of naval ECM systems and as "electronic aggressors" in naval exercises. These two aircraft were the last B-47s in service, and one performed the very last operational flight of a B-47 on 20 December 1977.
so your model is a very rare bird indeed. Excellent find!