The closest thing to model's dimensional properties is the
model's boundingSphere property. It gives a radius of an imaginary
sphere that contains all the vertices of the model; the sphere's
diameter is the distance between the two farthest-apart vertices.
However it includes the model's children in the sphere. Set
yourModel.debug = TRUE to see it.
You could loop through each model, add a mesh deform
modifier, go through each mesh[ ].vertexlist, keep track of each
max and min x, y, and z value, the calculate w, l, h from that. It
would take a little time... you probably wouldn't want to do it
every frame. But you could do it on a keypress or something.