This ship that I am about to present to you was designed as a "plot-device" for a hypothetical third season TOS episode that I envisioned being called
Hubris....
The episode would deal with the Federation building a new highly experimental vessel designated
USS Excellence. Her mission was to replace the Constitution-class as the premier deep-space explorer by utilizing a newer type of FTL warp drive. During the episode, the Enterprise was despatched to act as a "chaser" vessel to the Excellence, and observe her progress, but something (obviously) goes very wrong. When the Excellence engages her experimental warp drive the ship bolts like a bat-out-of-hell, into subspace and begins to rip a fissure in the fabric of space. To make a long story short, the ship gets destroyed with practically all hands, and the crew of the Enterprise attemps to same who's still alive while the orions attempt to scavenge the people and ship parts for sale.
Anyway, the ship is designed to show why intergrated nacelles have never really occured outside low warp designs, till TNG era's USS Defiant.
The large deflector, was also thought of at the time as a neccesity for the much higher than 'normal" relativistic speeds that the vessel would be travelling.
Well here she is:
USS Excellence, NX-1900Sketches to help fill out the idea: