Re: (beta) nvidia-settings not detecting VGA monitor correctly
I suggest dropping Twinview for now, and focusing on getting the CRT working at 1280x1024.
I still would suggest give your modeline a unique name. 1280x1024_75 isn't unique.
However, if the modeline you're using is resulting in the CRT not coming up, that suggests that its outside of spec. Can you verify whether a 60Hz refresh rate modeline works any better?