Back in 1974, TSR published a set of wargames rules based on Edgar Rice Burroughs' John Carter of Mars / Barsoom series. The booklet had only one print run, as they were sued by Burroughs' corporation for violation of copyright (back in the day, TSR was anything but IP savvy).
The booklet has since become something of a collectors' treasure, and fetches pretty high prices on the collector market and ebay when it shows up. There can be found PDFs of it floating about, if you know where to look.
Anyway, over at the OD&D Message Boards there is a forum dedicated to the game, and as things do there, discussion turned towards adapting WoM to OD&D. The task didn't seem that difficult at the outset; WoM is similar to Chainmail in many ways, and unless I am mistaken there are Barsoomian critters in Monsters and Treasure.
As these things do, the discussion took on a life of its own and a poster who goes by "Doc" put together a set of OD&D rules for Barsoom, and me being who I am, I couldn't resist creating an "official" looking supplement booklet. I used art from the original Warriors of Mars, because it seemed appropriate.
Anyway, you can download it at my website, as with all of my OD&D fan works. Enjoy!