More of that later, when I've painted the alternative loadout and when I paint my Kra'Vak...
So after asking online and having a look around I settled on the Hydra mech from Critical Mass Games. Craig very kindly sent me a few extra pieces so that I can use the optional weapons I bought as well as the standard weapons that come with the Hydra and a rather nice weapon that looks like a plasma cannon of some kind. (That's it on the left of the mech in the pictures).
More on the optional weapons in a later post. I think it will really change the look of the model.
The mech itself is a great model, very clean casting with little cleaning required and it goes together very nicely with plenty of scope for posing. I ended up putting magnets in the shoulders to allow me to switch out the weapon options.
Naturally, I swapped the ARC fleet pilot for a Kra'Vak pilot from a GZG model. He's one of their older sculpts, but will represent a juve very nicely.
Hydra mech is available here: www.criticalmassgames.com/default.asp?itemnumber=AFVH8a&cat=arcfleet&rtntag=vehicles