Tiki the core of the thing is going to be Basic Roleplaying, which is the core system used for both Runequest & Call of Cuthulu a couple of rather interesting supplement are avalible particularly
which is a source book for the wild west with suggestions to use it for weird west amongst other things &
which expands on the magic systems included in Basic Roleplaying itself
I intend to loot the other systems for ideas I would then rework to mesh with Basic roleplaying as they are all mechanically incompatible.
I also find playing the game helps give me a feel for the world & would suggest it to others especially as there are enough forces in the shop to to do this without getting drawn into it as a game.
Ginger