My theory is that the overall scale of the game was scaled down roughly 2/3 for HW2. (Based on comparison of the motherships) I can only presume this was because of engine limitations of some sort. There are those who think that this may mean that the unit sizes we've been interpreting as "meters" in HW1 were actually "feet" (which would make the Kushan Heavy Cruiser only 390-ish meters, still bigger than a Connie though
), but I don't buy into that one personally, again based on mothership size--making the HW1 MS only 2 klicks tall rather than 7 doesn't work for me, given that they're shoving 600,000 or so Kushan-sicles into the thing.
Also, it's long been accepted as "fact" that fighters and corvettes were scaled up in HW1, to make them more visible. (Maybe this also has something to do with why they scaled things down for HW2, I dunno--trying to second-guess what the guys who made HW2 were thinking, and what Sierra would let them do with what they were thinking, or indeed what they or Sierra would let them think is about as impossible as reconciling ENT as a prequel to TOS.
)
BTW, This post is offered is evidence that I can drag threads that are almost entirely unrelated to Star Trek off-topic with fanboy trivia just as easily as Star Trek ones.
The turrets, I think, can probably be faked with proper hardpoint and arc placement. It won't look as cool, but it could probably come close. I'd be glad to help with that if the model could actually get made. And, just to show that I'm trying to help, I'd be willing to provide a converted-to-.3ds version of the stock HW model (assuming I can convert that properly, but I
should be able to) as reference if anybody wanted to try and make a new one.