The more I think about this, the more I see that I do have a big problem with the idea of making bootleg manuals. How many people have been burned by overpaying for Sapphire boots? This is what will eventually happen, no matter how good the intentions are.
Putting a disclaimer on the back of the manual isn't going to protect a buyer that only sees a picture of the front. Are you guys really going to expect every seller to now provide front and back scans of every manual? What about scans of every page? Seriously.
I can relate to wanting complete stuff, but there's got to be a line! If you're going to offer an alternative, it should be that - not a bootleg. I think you could just as easy make a retro cover (maybe with a small 1/8" border) around the image (you could use the color associated with the game type even.) Problem solved.
Sparky, I really hope you think this cover thing through. It's no different than someone getting bootleg boxes made. It will happen. How will you react to that when it does?
This time - I voted. NO, not they way you show them!