There is a fret of PE in the kit which provides replacements for some of the plastic parts which are too large (in scale). PE allows for a finer part which may be beyond the limits of technology in styrene. These include ladders, hatches, support brackets, prop guards, and similar items.
The upgrade PE set available for the '42 Buchanan includes railings, both inboard rails and deck-edge rails with mesh. There is also a pre-formed MK37 fire control radar antenna with stiffener brackets.
There are no PE masthead radar antenna nor PE latticework for the midship searchlight stand in either fret.
The choice is up to you. There are no other dedicated PE sets for either Buchanan at this time. There may be one from GMM in a while. It will likely be more expensive than the upgrade PE set which is currently available and/or repeat items which are in the basic set.
I'm thinking that the 45 Buchanan may be the better starting point. The Emmons and other Gleaves destroyers were converted to DMS in late 1944. Among other things, the 1.1 inch gun on the aft superstructure was replaced by a pair of 40mm twins by the time they left the yard following the conversion. The twin 40 layout is included in the 45 Buchanan. The 1.1 inch gun layout is in the '42 version. Less destruction before construction.