I was looking around the internet just now, and I came across a website that featured fake NES cartridges made by numerous people, and one of the ones I came across was this one:
http://neszone.nintendohost.com/funstuf ... systar.png
I can see why the guy decided to use a Tengen cart for the template when he made this, because there were some Famicom ports of some of Sega's arcade hits released in Japan that Tengen brought over here.