Does it actually need to be a 1920x817 signal, or can it be a 1080p signal that is only rendering 1920x817? (letterboxed 1080p) The latter is easy to set up with an Nvidia card.
It's unlikely that you will be able to go over 60Hz with HDMI - most devices will only accept 24Hz, and then internally display a multiple of that. (e.g. 48/72/96/120/240Hz)
If you're lucky, and your display supports 50Hz, you might be able to get it to sync at 48Hz. So far, I have only been able to get my current display to sync down to 48.501Hz - any lower than that and it reports that the signal is unsupported.