Apparently I upgraded at the wrong time. (coming from mountain lion, doing a clean install of Yosemite with a brand new EVGA 970 GTX)
It seems some GeForce owners that updated to the current 10.10.3 very recently had their nVidia drivers voided. Current Build is 14D136 but nVidia's latest drivers only work with 14D131. You're all correct, you need to trick the nvidia startup kext to see back at the 14D131 version.
For some editing kext did not work. I suspect that they were running IDE hard drives (not SSD) and not in dev mode as a result. Anyhow, this tutorial outlines what to do as a fix. Very thorough. I haven't gotten through the entire process myself as I still am repairing permissions and the tutorial goes on to suggest reinstalling the 10.10.3 combo update afterwards. Not feeling particularly keen about that as those combo updates always tend to kill my OS.
FYI, my EVGA has 2 working DVI ports and no working HDMI or DisplayPort. (as of nVidia drivers for 10.10.0) I was hoping that having the latest nVidia drivers would magically grant me a working HDMI or DisplayPort so that I can get back to having triple displays again. My 27" Cinema Display is collecting dust over here...