Here's the "crop mark" script I use with the latest version of Illustrator... I've been using this one for years. Or if you need one that works with an older copy (CS6 or something) just do a Google search for "MakeCropMarksAI.jsx"
In Illustrator, use the File > Scripts > Other Scripts function to open it, or you can simply keep a copy of the .jsx file on your desktop and drag the script to your artboard when needed. A pop-up dialog will appear. The trick here is to use a negative number in the offset values (see attached screenshot). This will give you "inline" crop marks instead of exterior ones.
One other quick thing to keep in mind about crop marks. Technically, you are adding a center line stroke to the crop marks -- so if your artboard is already resized to fit your artwork when you add the crop marks, half the stroke thickness will overlap the artboard edge -- so you can either adjust your artboard size accordingly, or simply give it a thicker stroke to make sure enough of the line is visible on your print (e.g. 2pt stroke = 1pt visible) -- if that makes sense.
Oh... and one more thing... since this is a .jsx file, you can open it up in a text editor and change the default values to fit your workflow. That way you don't have to key in the values manually each time.