.6 mms between the holes leaves no margin for error, and hardly any strength in the wood . If I have to drill so close together in brass, I make a template in steel, just a small piece with the holes accurately done with a pilar drill.
If I've understood you correctly I would be looking at a way to use 3 mms holes maximum and altering the davits.
A picture of two of what you are attempting would help get a better answer.