The DS-1280ZJ-S is chunky because it needs to house the pigtail connections and RJ45 crimp. Two cleaner routes for a turret like the DS-2CD2345FWD:
1. DS-1280ZJ-DM8 (the "DM8" base sparkymarka mentioned) - it is shallower, neater, and takes a standard M20 gland straight into 20 mm conduit or...
Fair play to you for helping your elderly neighbour out. Classic Accenta G3/G4 and modern universal SAB sounder mismatch is very common on these older systems.
Here is the physical wiring reality of what is happening:
Your old 30-year-old bell was likely a passive sounder (only powered when the...