Speedy,
I did some rooting around in my B-29 stuff and I
might have found your airplane. The 497th Bomb Group had an
Outhouse Mouse, serial 44-70119, and she was later converted to a SB-29. I'm going out on a bit of a limb as far as the name goes, but I'm guessing that she kept her wartime nickname postwar. Here's a ship listing for the 73rd Wing with her I.D. toward the middle of the list.
http://b-29.org/73BW/bomb-wing-data/nickname.htmIt may be a different airframe that ended up being named
Outhouse Mouse during the SB-29 days, but the coincidence of name, serial number, and conversion to ASR duty are worth investigating.
Of the four airplanes you listed earlier, Mann has no record of 44-61671 being active after 1951 and 44-87761 having never been converted to SB-29 status. These results are per the Individual Aircraft Record Cards. The other two were definitely converted.
More later,
Scott