The blocks on top of the ribs look silly, should just axe those. The ribs themselves would look stronger if they connected to the main hull instead of simply hanging over it.
I'm not digging the armor plates strapped on to the engine, they just look taped on and like they're about ready to fall off with the rest of the engine. A better idea would be to work the panel covering the rear of the model (the one above the windows) into a protective plate for the outermost engine. It would make the whole rear of the thing feel more solid and flow better, you might even be able to get away with keeping the side panels if you do so.
You can also always push the outer engine closer to the main hull a bit, in case lengthening the top armor plate too much looks too tacky.