I always in the past thought it more a star destroyer tacked onto the enterprise rather than a Klingon ship... But then... I'm tainted by having seen the original 1970's ship... and the knowledge Ralph really did work on the Star Wars Star Destroyer.
Here is one link with some images of it.concept art.
http://io9.gizmodo.com/5721854/ralph-mcquarries-lost-concept-art-for-a-star-trek-movie-in-1976-1977/
The Matt Jefferies design (aka what some fans refer to as Constitution II or the failed Constitution refit) was much closer, but still distinct from the final one chosen... (note closely the older saucer design, the torpedo tubes, and the exact shape and look of the warp nacelle, which are not same as the design finally used)
http://www.modelermagic.com/wordpress/wp-content/uploads/2014/10/phase_ii_1701-007.jpg
Andrew Probert was brought in, and took the Jefferies design, and made his own distictive and more extensive remake of it, it was his design that eventually became the movie model.
One has to remember with the designs of the 70's by Ralph and Matt... they were not originally to be for a movie at all... Paramount was gearing for a new low budget series (called Star Trek Phase II, the scripts were eventually released in book form for fans interested), not a movie at all... they changed their minds last minute (literally, they even had the contracts altready signed and had to pay out on it). The change to movie expanded the budget and created a need for far more detailed models.