Hello, the Ninja is compatible with Gigabyte GA-P35-DS3R (mine is a revision 1.0)
BTW, that means that GA-P35-DS3P is compatible as well, layout is the same around the CPU.
I was initially concerned that it would touch a row of condensers, but it turned out fine. The orientation I used is the one that leaves the least space between the Northbridge radiator and the Ninja heatpipes, I tried both ways.
Here some pictures:
All the best !