Okay this is good info.
I looked at the SUR data with the FL model tool in the first reply and am a little overwhelmed by the data dump. Also did some more research and the math required to calculate volume of a 3D model from triangles seems pretty intense. It also requires that the model be fully closed, which is not the case with many of the models.
Now that I know the numbers are meters, it seems like a pretty easy thing to get dimensions by adding and moving hardpoints. IE, wingspan, nose-to-tail, etc, can be determined by adding hardpoints and manually recording the offset. Once I have that data I can make oblong spheres for consistent relative size.
Not something that can be automated right away, but at least its a usable technique to get a basic shape. And if I add reference hard-points to each model, then it probably can be automated.