Wow - I just had a shufti at the new BoLS Arbites Codex - what a corker! What's more, they've created their very own MSTTD - the 'Black Maria'!
This, on the one hand, is awesome, and on the other, is illustrative of what I was trying to avoid with my Wyvern - though I don't really think I achieved it. I deliberately wanted to steer clear of any whirlwind variants, as they just looked a little too neat and a little too powerful. Also, I wanted to locate the missiles further back. FInally, I deliberately kept the aesthetic link to FW's support sentinel, so I had those rules ready-made.
In retrospect, though I want double missiles, Grey_Death might be right to suggest that one port-mounted set could have sufficed. The wyvern is looking maybe slightly more powerful than I wanted.
Then again, not only does the Black Maria look "sweet as" - it also has a nifty thing going on with the rear lasgun ports. It's not too late to change mine: could I do something similar and imaginative with magnets, perchance? Hmmm...