The problems start appearing once you try assembling the ship. Test-fitting the prow only reinforced my decision to scratch-build my own custom prows for my Vengeance hulls anyway.
There's no way I'd be able to attach this without 2-3 pins for stability and a whole lot of modelling putty... so I'm going with plan b: scratch-build my own prow, attempt to replicate it as best as I can twice more, and then install them on my Retaliator, planned Exorcist, and planned Vengeance/Avenger swappable kit (because it won't be hard at all to design it so I can pop off four magnetized lance decks and replace them with four magnetized weapons batteries).
My first bit of advice if you try building one of these on your own: put two blobs of paint on the engineering/bridge section of the grand cruiser and then mate up the gun decks to that section like I did in the image below. That'll make it really easy to drill in 4 aligned holes and pin the ship together. I use paperclip sections for this; it's a nice thick solid bar that isn't going to bend or break anytime soon, and will help secure the ship sections nicely.
I'm still working out the exact shape and dimensions of my replacement prow. I'm thinking I want it no wider than 7/8 in., and about 1.5 in. long. The Veangeance's prow is about 1 in. wide and about 7/8 in. long, not counting its ram spike, and for comparison, the Repulsive's prow is about 7/8 in. wide and 1.5 in. long.
Of the two, I'd rather go with the Repulsive's dimensions and holding it up to the model out of curiosity, the ship definitely benefits from the narrower, longer profile. I'm a little torn between whether I want to have the prow flare slightly like the plastic chaos cruiser, or whether I want to simply bring it back flush with the gun decks and use something very similar to the Repulsive. The more I think about it, the more I like the latter option. I think I'm going to make the sides a little less steep than the Repulsive's, just to bridge the design gap a little between the Imperial and Chaos ship designs. I'm also debating on whether I want to mount the torpedo tubes in the prow, or under it (the BFG:R ship rules allow you to upgrade the Vengeance-class hulls with torpedoes or an improved sensor array if you want), but for the Retaliator I'm definitely going with the sensor array and I'll be running a bunch of antennas out of the prow's sloping armor when I'm done with the basic shape. I also want to splay the arms of a chaos star across the prow on the chaos version, and sculpt the imperial aquila (or maybe a winged skull) onto my eventual imperial ship prows. I feel like they need something to link them in, and some of the original Battlefleet Gothic artwork in the book depicts chaos ships with massive chaos stars on their prows, and I'd like to try my hand at that. I'd show you my progress on a plastic scratch-built prow, but I've already junked it after realizing I'd built it way too wide. Something to pick up with and work on tomorrow night!