kernel frame buffer support for GTX680?

While trying to debug issues I am having with the Nvidia drivers on Ubuntu and Fedora when installed on a 2008 Mac Pro with EVGA GTX680, I decided to try a manual installation of the Nvidia 960.54 drivers using the instructions from...

The step which hangs on my Mac Pro is the run level 3 reboot using a kernel image built with the nouveau kernel module blacklisted and the ‘rd.driver.blacklist=nouveau’ appended to GRUB_CMDLINE_LINUX in /etc/sysconfig/grub. The boot produces a single white hyphen on the screen, a lot of disk activity and not other text or prompts.
What is the status of the default frame buffer support in the 4.15 and 4.18 kernels for a GTX 680? I find it hard to believe that one has to use the nouveau or the nvidia kernel video driver instead of fbdev. I should also note that this card is the 02G-P4-2684-KR Superclocked with backplate that has been flashed to the official EVGA GTX 680 Mac ROMs for EFI support of the Mac splash screen and option key boot selector. Without flashing these ROMs, selecting the boot drive is a rather painful process on a Mac. Other than these issues with the frame buffer driver and a black screen with the nvidia drivers installed by rpm fusion or ubuntu, the card works normally with the nouveau drivers in Linux, under Windows 10 and under macOS High Sierra or Mojave (where the Metal support is detected).
Any suggestions on workarounds for using the frame buffer with nouveau blacklisted? I wanted to try the manual nvidia installation in order to see. if it made a different in the nvidia black screen issue (which I suspect is an orthogonal problem to the frame buffer one).