Deep Intrigue

Now and then on the blog, we like to throw you a curve ball. Crowdsource a problem or two. Just before I went on my hols, the irrepressible Woodstock found  a strange toy on ebay US which he thought he'd dangle seductively before me, see if i'd bite. At the time, I didn't and the auction ended without any interest. it was listed as a Voyage to the Bottom of the Sea 'Undersea Crawler', in the vein of the classic sixties Remco toys. The seller wasn't entirely sure of its provenance, but listed it at a good price and described it adequately. After it wasn't relisted, I contacted him and bought it at the opening price. It arrived yesterday, in a kit form and a deal larger than I had expected. From the pics, I thought it must be around the same size as an average Dinky car, but it is actually about 8-9 inches long. Putting it together without instructions was fun, although the build was cleverly made to snap together without glue. This makes me think its a modern japanese toy. However, I was left with several pieces over and nowhere to fit them, including a crank handle and the large grey rectangular piece that sits on a ball joint sticking up on the back. I added two orange solar panels to cover the bare gap. Also, the bulb at the front looks like its missing a cover, so I added one of my own.
Overall, its a great model, zips along with the light glowing at a fair pace, but theres no makers marks at all. The sprues were alphabetically coded in english, but thats it. Anyone got the slightest clue what it is ?