I'm writing up a set of solo rules for a Forbidden Lands adventure site and I've got a good start on a draft document and eventually I'd like to put it up on DriveThruRPG when it's ready. I based the solo adventure site off of The Hollows (one of the basic sites included in The Gamemaster's Guide), and re-used the names of characters & locations and some concepts for events, but re-wrote everything from scratch. I'm curious how much from the official settings can we use when writing up our own material?
I'm assuming the safest route in this specific instance would be to just rename everything and file off some more edges to remove any and all similarities, but I am curious how close can you come to published content? Obviously we need to refer to people, places, and things from the setting, but how much is too much?