Shadowrun engine legality, How legal is it? Options

[Shadow]

I am not sure if this is the right forum to be posting this on so I apologize in advance if I am in the wrong place.

Shadowrun has a really cool, and versatile system. Sure some of the specific rules bite, but the system as a whole is really good. The idea of TN's and varying degree of difficulty based on the number of successes you get is good stuff. Not to mention the un-precedented control over character creation (point system) and of course how you advance is pretty marvelous.

Now before I get going let me say, I love the setting. %100 the best RPG setting EVER! Lately though I have been longing for those bygone days of Traveller and Star Frontier. It has been years (like 20) since I played either and I am really not interested in searching ebay or other sites to find the (out of print I am sure) rules to them. Nor do I want to teach them to my group.

I would however like to adapt the core SR rules to a more hard sci-fi setting. Something 600 years in the future so I have lots of leeway for my imagination to run wild. I have a pretty good idea (Thank you Stumps and LM for inspiration) and I would like to flesh it out using the SR core rules.

However; if I spend countless hours working on this system, and mod the SR rules to it, I may want to post them on the web for others to enjoy. At that point (hypothetically of course) would WK or FP step in and shut me down? I am not a publisher, lawyer, or affiliated with anyone on those respective businesses. like most people I have a hazy concept of copywrite laws. I don't want to steal or plagiarize anything, just use some of the concepts from the BBB in my mod.

So what I am talking about is writing a mod for the SR rules to adapt them to a Hard Sci-Fi setting. I would use nothing that is setting specific (magic, elves, dragons, etc) from SR, just the core rules.

Anyone have any incite they can give me?