Hi Booleano, I'm sorry but I'm not understanding very much of this.
First off I'm seeing 6 objects in Green, not 3 like you wrote and the objects are stacked up on top of each other.
Next thing is I don't understand what you mean by doing a boolean difference to a specified dimension. Is it a 4mm radius fillet that you want to have that you are showing in CC.jpg ?
If you're trying to create a "mould" I managed it by putting an exact in-line block for the boolean with the rear section
a single multi-block boolean failed for me
I presume the others would work this way too and then merge them.
It's true that the 3 objects are duplicated, but to fix it, you just need to delete the extra 3, leaving only 3. Could you delete them? That way I don't have to send you the file again.