The head design of the ninja Spin looks to be pretty close to the Do-It Ultra Minnow Jig Mold. I can speak from experience that trying to make a decent mold for lead is not the easiest thing in the world to do and if that Do-It mold is remotely close to what you're looking for (or any of their others) I'd recommend modifying it to take a spinnerbait wire. Fill the voids with JB weld (hook eye) and take a file to cut lines where you want the wire to sit.
I've tried bondo and JB weld in the past for duplicating items - with limited success and am about to go the 2 part silicone route on a couple projects I am working on. BTW, I got the best results from bondo and here's a quick run down of what I did... I took an old hilts mold, drilled out the center of each side on a drill press larger than the bait I was reproducing. poured in the bondo, sunk the jig halfway down, let it dry (you'll need to apply some sort of release agent so the bait doesnt stick) Pulled the bait and sanded it down flat. (a razor blade also works well) Replaced jig - coated entire surface with release agent - poured bondo in the other side of the mold cavity and closed/clamped the mold. IN theory, when you open the mold, you should have a pretty decent cavity.