Newbie SW 2004 Cutting 3D Parts

Hello,

I am trying to cut a premade part in half using SW 2004. Main problems:
-The part is nowhere near an origin nor a plane of any sort
-The part is made entirely of curves and curved surfaces, so there is no way to create reference geometry.
-Filetype is x_b v10, don't know if that matters but its the only way I could open it since the part was created in SW 2012, which I do not have.

Any ideas?

Thanks,
Jess (flame2)