Belated update because my muse disappeared three weeks ago.
I developed modules that could fit on the warp nacelle hardpoints, then added four more of these hardpoints to the primary hull, rated for the same mass and power handling as the nacelle mounts. Default fit would be a pair of science pallets and a pair of very large double-ended phaser cannons, easily tripling the ship's long-range firepower both fore and aft. Science pallets can be mounted anywhere on the ship, while the phaser cannons would be preferentially mounted directly to the nacelles to directly tap main power. Extra shield modules can be installed into the science pallets.
Also added a reinforced bumper pad to the ventral fantail. Simulations revealed the slightly horrifying possibility that planetary landing of a heavily aft-loaded Catalina stardrive section with no saucer attached can cause the ship to rock back on its rear landing gear [not shown] and become the world's biggest taildragger, sustaining massive tailstrike damage to the shuttlebay and fantail in the process. Bumper pad will be rated to bear the full weight of the stardrive equipped with 7-11 nacelles and full rack of four heavy phaser cannons. A scary situation now becomes an interesting design quirk. Normally, mass-lightening and structural-integrity field technology would render this problem moot, but this ship is designed for ruggedness and fault-tolerance in hostile environments.
I'd like to thank
for his immense help with this iteration of the Catalina design.