You can use any water block for a 680.
No, not just any
block will work.
You have to figure out a few things about your card first, mainly whether it has a reference design PCB or not. More detailed reviews on the card will tell you which PCB it has, though you can usually just visually inspect an image of the card's PCB versus a reference one to tell if it is or isn't.
Given that its an MSI (known for over building their cards) and a 4GB model, I suspect not, but it might be.
If its reference design, then any reference 680 waterblock will work on it.
If its a custom PCB, then you have to make sure the block your getting is compatible (you can email the block and card manufacturer to find out) or pursue a universal solution.
I suggest you read the water-cooling sticky, it has a section on GPU water-cooling.http://www.tomshardware.com/forum/277130-29-read-first-watercooling-sticky
Another good resource. Punch in your card and it will tell you if its reference PCB, and whether there are any compatible waterblocks (EK only) that will work with it.http://www.coolingconfigurator.com/