Mate I love your enthusiasm, but just tread carefully.
I know how this sounds but I would consider doing this via the right process and channels and then you have nothing to worry about. I believe that the person you are referring to demands 10% of your profit or takings or you could give him 20% of the stock you produce - it may be vice versa. That way the decals would be endorsed by Williams as such and your butt would be covered and you can still produce top notch high quality decals that prove your point.
I would love to see you get this done, I just don't want to hear you have any dramas. There are few guys on this forum that I am sure have some stories for you.
As for decals sets...
BSD
Police Force, especially the POLICE FORCE letters on the topper
