Bassman400

I recently purchased a Yamaha 4 string from e bay. The guy who was selling had no idea which model/number it was. It sounds superb and for the money I paid it is the best value bass I own. I would like to identify it though and have scoured the internet to no avail. I know it was made in Taiwan and has a serial number NJ13140, which the Yamaha site tells me dates it from either 1987, 1997, or 2007. I'm guessing it's the middle one. The headstock is like no other 4 string Yamaha I can find. It has 3 pegs on top and one bottom. Have hopefully attached some photos and hope someone out there can satisfy this bass anorak!