The most rare and remarkable of the three books is Boot Hill, which is a first printing from 1975. Someone correct me if I'm wrong, but I believe that this is the third roleplaying game ever published, behind Dungeons & Dragons and Empire of the Petal Throne. This little brown book is pretty hard to find, especially with the tear-out reference sheets still intact. I have to admit that I've never been terribly interested in Boot Hill or any other historical games because wizards and weird science are my thing. This game looks like a lot of fun though, and I could see myself running a few weird west shoot outs in the near future.
I also picked up some early 1980s Boot Hill minis off eBay for $1. Cool!
Here are pictures of the artifacts...
CLICK IMAGES TO ENLARGE
Unlike most of the other little TSR books from the period, Boot Hill includes numerous ready-to-go maps, scenarios, and NPCs.:
Rare double-page tear-out reference sheet:
TSR Boot Hill minis c. 1983: