Page #4 DIY BED Instructions
Next, make measurements to locate where the first hole is on the leg and draw an “avoid line” on the board, just for reference. You dont want to cross drill anything, if you do… the bolts won’t insert properly. If you measure from the top of the leg, remember to account for the 1/2″ gap. Draw a line 3″ inches from the edge because you will be drilling 3″ away from the edge into center of the leg.
With your “avoid line” and by the 3″ inch mark, drill a hole and insert a bolt between 1 1/4″ to 1 1/2″inches from the top and another one 1 1/3″ to 2″ inches from the bottom.
Here I am marking the lines to avoid. 
Remember to check to make sure your lines are straight, secure both pieces, and to drill straight and steady. After your first one, you have three more sides to do.
Note: I did have trim/sand 1mm-2mm off the edges of the short (head/foot) at mock assembly.
Getting there!