Creative counts-as for Chaos Daemons in 40k

[Herr Major]

I absolutely love the new Arachnarok Spider model released for the Fantasy Orcs and Goblins codex, and think it is filled with great modeling potential. While I have never completely embraced the counts-as phenomena, I was struck with an idea of how I could use such a great model in my Codex: Chaos Daemons army in 40k, but I'm unsure about the rules. Let me state that I normally only play in casual games, and know the protocol for getting counts-as units accepted in a tournament style game, but when the model it is representing has no official model or base size listed, there is a nice gray area to work with. While I originally wanted to use the model as a counts-as Great Unclean one, it was pointed out to me that the generic "Greater Daemon of Nurgle" is the "accepted" model and base size. My question is thus:

The unit in the codex Ku'gath the Plaguefather has no official model (outside of, I guess, that giant resin model from forge-world) and maybe the Arachnarok could fill the role with some nice creative modeling, green-stuff, painting, etc. Provided the majority of the model could fit on a 40k base such as a Stormraven/Valkyrie/Trygon base, would it be an acceptable counts-as model as far as model and base size? I think it fits the fluff in a very cool and creative way. Just don't glue on any goblins, green-stuff on some boils & nurgle symbols, add Nurglings to the base and voila. You now have a giant daemon spider running around dripping poison on its enemies and spawning little nurgling/spider things!

So in summation, is such a creative thing acceptable rules wise in the game? Thanks for reading!

[Connjurus]

I love it too, but Ku'gath is stated to have started out its existence as a Nurgling - I don't think it fits the fluff.

I, for one, am going to convert it into an Organic Soul Grinder. :P

[Herr Major]

Hmm...maybe the fluff got thrown out the window a bit but what about modeling such things in general? As far as size of model to base ratio, especially when it is unrepresented in the model range/codex?

Thanks!

[isotope99]

I say do it. The only thing that's going to hang off the edge is the legs. Model it so that it is supported at the belly and you could probably even squeeze it onto a normal monster base. Although I would agree with Connjurus, the soul grinder is a better fit size-wise.

If you're worried about WYSIWYG, write what it is on the edge of the base.

Generally, larger models are a disadvantage to the owning player with TLOS.
I saw someone use a converted trygon as a nurgle daemon at one of the throne of skulls tournaments.

[DrWobbles]

The arachnarok has great tyranid potential.

[TSINI]

The arachnarok has great tyranid potential.

definately, i've been looking at the pics thinking of ways to remove 2 legs and turn it into something, it would suit a tyranofex or something similar, although i think it would make a good Horvigon (like a tervigon but for hormagaunts) as this would suit my army fluff very well.

[Monkey]

I think the Arachnarok works wonderfully for the Daemons. I am currently building a Daemon List, and I plan on using the giant spider for my Keeper of Secrets. I'm going to kit-bash it and the Daemon Prince to create some sort of centaur-esque monster. I plan on trying to use a standard MC base since, as was stated earlier, the legs are really the main issue and the body doesn't look like it would exceed that base's footprint by too much. I'm loathe to use the Trygon base because it will cause too many Difficult Terrain tests and increases the likelihood of DS mishaps.