Hello,
 
I know this might be many years late, but I managed to find a waterblock for the 770 4GB (04G-P4-3774-KR) version that does not require any modification!  The water block is: Watercool GPU X3 series.  They still make these.  I got mine from ModMyMods.  The model number  is: WC-15538-D , name: (Watercool HEATKILLER® GPU-X³ GTX 770 "Hole Edition" Ni-Bl).  I will be posting some photos very soon.  I know this is late for many users since people have moved away from the 770 4Gb, but I bet this info will be valuable to some.  Watercool even lists it as not compatible, but it is 100% compatible.  The only extra thing you can buy is 5mm and 4mm thermal pads if you want to use the back plate to cool some components and the VRAM which I will.  The back plate model number is: WC-16007 , name: (Watercool HEATKILLER® GPU Backplate GTX 7X0)   Here are some photos of it so far.  The 770 is a great GPU and still can run things great today.  In my post about the X99 Monoblock, it goes to show you that there a compatible blocks out there, and that there simply is lacking info on compatibility.   I will be installing this waterblock soon in another system. 
 

 

 

Here is the water block fully put together and as you see, it fits perfectly.  Going to be installing this in a secondary system soon.   
 

 

There are 4mm and 5mm thermal pads underneath the back plate for the VRAM modules.  You will have to get these thermal pads separately. 

 
 
 
 

Here is the thermal pad layout.  The backside of the card is where I used 4mm and 5mm thermal pads.  I simply followed the arrangement of thermal pads on the  EVGA back plate.  
 

Thermal pad arrangement on underside. 
 

Back plate side.