Fortunately FAB 3000 does have a "STEP" output, which can be loaded by Solidworks and all other major 3D CAD software tools. Please perform the following:
1. Start FAB 3000, and import your gerbers.
2. Go to menu: File | Export | STEP...
3. Assign layer width(s).
4. Click Next, and assign STEP file name.
5. Start your SolidWorks (or other 3D cad software) and import the STEP file.
Here's a movie tutorial showing all required steps: