http://empireminecraft.com/wiki/slot-shop-signs/ Slot one is top left, slot 27 is bottom right. For a DC, bottom right is slot 54.
[Name] [Amount] [Price] [Slot 1] and keep it on the left of the chest above it, and do slot 27 for it to be bought from every slot, dont know if this is what you meant but yh?
The top left most slot is 1 and the bottom right most slot (in a dc) is 54. See: http://empireminecraft.com/wiki/slot-shop-signs/ for more info Scruffy has a video here as well: https://www.youtube.com/watch?v=tSH5VP31WKQ HTH