Okay, further research has shown me that RA2's Havoc engine must be expecting left-handed coordinates, unlike VRML and 3D Studio Max's right-hand coordinate systems.
This means I'll have to negatively scale all x coordinates and flip all normals. May as well include that rotation around the X-axis as well then (VRML has Y as up, while 3D Studio Max sees Z as up).
Update: Negating the x-axis, and changing the face vertex direction solved the mirror image problem. I still have the rotation problem though; There must be a way to convert the transformation matrices.