Ironically enough, I am currently playing in a RQ6 Mutant game, run by one of my Swedish friends. We simply rolled up characters as per RQ6, added a few technical skills for sciences like Electronics, then rolled on the mutation table to gain weird powers. For guns we just use my RQ6 Firearms document up on the website.
I think the GM creates monsters by picking the nearest fitting creature in the RQ rule book. Other than that we're happily looting bunkers, causing nuclear meltdowns and shooting other mutants. Great fun!