It took some training and skill to operate the ASB radar. It was replaced by the APS-4, which looks more like a conventional radar. It could be mounted on an existing bomb rack and jettisoned if needs be. Airplanes wired for the APS-4 received an "E" suffix indicating modified electronics. It is sometimes mistaken for a fuel tank or a bomb. (For more on the APS-4, see http://tailspintopics.blogspot.com/2014/11/things-under-wings-anaps-4.html.)
The APS-4 was replaced by the APS-19, a more capable radar, for most new applications beginning in 1946. (The TBM-3S conversions used for the interim ASW hunter/killer team were still equipped with the APS-4, however.) When provisions for the self-contained radar pod were standard, as in the Douglas AD-4, no E suffix was required. In general, when the APS-19 was installed in night fighters it was an integral part of the aircraft rather than carried as a pod. The Grumman F8F was an exception.
The APS-31 appears to have come in two different flavors from the standpoint of antenna size. The APS-31 or -31A carried by the Grumman AF-2S pod was similar to the APS-19 pod except that it had a longer and more pointed tail cone.
The following illustration is based on drawings that aren't up to my usual standards and pictures. Better information would be appreciated. e.g., it appears that there may have been an AD-4N pod radome that wasn't quite as "blunt"as shown here.