Leaflet.js with a non real world map! Coordinates

I'm working on creating a map of Day Z (the game) with leaflet JS and want to be able to plot items on the map using the in game coordinate system see http://dayz.ollieb.net In game the top left coordinate is 000 000, then 001, 001 where units of 10 represent a grid so 010, 010 would be the top left "grid" (similar to ordinance survey). How do I create a method to convert the provided coordinate systems (either points or latlong) to work on this way. Basically they just need to go from 000, 000 (top left) to 145, 130 (bottom right). Currently I am having trouble using lat/long as it curves to compensate for the projection and points (x/y) seem to change per computer! How can I take an in game point and create a marker on the map at that point? Presumably I need to tell Leaflet.js what "number" the top left and bottom right of the map are somehow? Sorry for the lack of understanding, I have read through all the docs and can't see anything like this mentioned! See an example here: http://dabrothas.net/sei/daisy/index.asp?mode=mark&z=3&x=-109.2294921875&y=73.49222029152183