Here is the complete (extended) Desolator upper hull on top of the Emperor lower hull. Design and space conflict issues will have to be resolved the in engines/rudder area. This is really just an enlarged grand cruiser in its design and looks to me to be a good direction for the VS assuming the engines rudder area can be resolved.
Note that four Chaos weapons bays are the same length as three Imperial weapons bays.

Thank you for putting these together timdp, they are very useful. The one you show here is very much where I was heading from the discussions we've been having in this thread. My feeling though is still to go with an up-scaled prow based on the Repulsive prow, 3D modeled and printed. Essentially I am imagining the Repulsive prow made slightly larger to address the concerns of fitting, mentioned above, and to add some structure below, similar to the area that has been stretched in your Desolator image above. I will model this in either Rhinoceros or Sketchup when I am back from Sicily next week.
In related news, I have now managed to purchase a (painfully) expensive Repulsive from eBay, which will form the basis of the 3D model and should make modelling that much easier to reference. I will of course be posting work in-progress images here.
I have also started making enquires about 3D printing services.
imakr have a physical show room near me in Clerkenwell, London, but their machines there aren't really of a high enough resolution. I have had a look at
i.materialise.com and there is of course
Shapeways.com, but I've not had expeirence with either. I may ask what people where using over on TacComms as that always looked excellent.
As always, thank you all for the invaluable input!