Legality of homebrew digitally "published" campaig

[Mana Trance]

Many, many years ago, I created a D&D knockoff RPG that I posted on the Net. The rules were horribly similar to OD&D's. The setting itself was kind of novel, with dinosaurs running around with dragons, raptor-riding tribal warriors, and other fun things.

Having recently become enamored of C&C, I'd love to rewrite the whole thing as a campaign setting for that game. I want to put it online as a free PDF. However, I'm uncertain of the legal footing I'd be on. I have no intention of selling it, but I don't want to end up on the bad end of a sharp stick for including such things as replacement classes and races.
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Ben Overmyer
Artist & Web Designer
http://www.manatrance.com