Charlie,
I use fusion as a Second pass program. As I am very well versed in Creo/Pro-e and Inventor, it makes sense to work in those to build the 3D models.
Fusion allows the import of so many file types it is very easy to bring a model in and then just use the CAM side of it.
For your application, you may benefit from learning how to build free form surfaces in Fusion if you want to use it as cad. This is not as difficult as it sounds it just takes time and knowing what to look for. You can also use the flexible modeling elements where you create nodes on a primitive (eg, sphere, box, torus) and pull them into a known shape.
https://www.youtube.com/watch?v=lt7mD8ErvJY
With your existing CAD, can you export a 3d DXF file? If so, you may be one step ahead of the game.
There also is the option to create "loft" features between strategically placed sketches. You create sketching planes at known distances from each other and place a x-section sketch on each one. you then extrude between them. Not sure if it gives you full control over the final object but it can be a start.
https://www.youtube.com/watch?v=QJCtZ0-St_I
Then the cam stuff is simple in comparison.