Having converted the Black Company to Rifts and Deadlands before, I can say that it is possible to role-play the books in a setting ina realistic and faithful to the books manner. Rifts, because at the time I was playing that, and playing it with emphasis on the core book (mean grim and gritty), and Deadlands, when I was into the system, is almost perfect for a BC campaign, a humanocentric world that is dark and full of fear and terror, just ripe for the Lady and her minions.
An official Black Company system was underway years ago, but the company has dropped from the limelight. As Tor Books are sensitive about copyrights and mention this in their FAQ, it would be a good idea to at least get their blessing before going too far. Especially the bit where they mention that one is still violating copyright by using copywritten material in a not for profit scenario, and they mention rpgs in this.
I am not intending to hamper the movement, quite the opposite, I would like to see it move forward and it wouldn't hurt for someone to ask permission of Tor before proceeding too far. It is quite suprising someimes, the permission you get when you just ask.
hellbender