Personally, I wouldn't do that kind of modeling job for free at all; and offering royalties on a game that you say will go commercial, isn't any comfort either. You're talking about quite a few hours modeling (as Wyatt said), as well as just as many hours creating the UV Map, followed by long hours texturing it....only to find out that your work can not be shown because the image is stolen. You should know by now that people here are all over the net, and can spot stolen things immediately.
I'm getting pretty tired of certain people around here wanting everything for free. It's one of the reasons why the model pack I am making will be the last freebie I do here. Normally I just don't bother posting in these types of threads, but do you
seriously think anyone would do something like this for free? It might have been possible if someone could put the finished product in their portfolio afterwards, but not if it's a stolen image.
-Keith