Consider the following:
The deck height under the nacelles/pylons, appears to be close-to identical to the height on the original Excelsior-class design. Add to that, your "Sovereign-style" nacelles appear to be nearly double the length (and thus double the mass) compared to the original Excelsior-nacelles.
So yea, you -should- consideer adding more mass to the ships rear end, or consider smaller, sleaker nacelles.