Stereoscopic headsets as monitors

Hi, I'm thinking of buying one of these headsets for stereoscopic experiments, and I'm wondering how they present themselves as plug'n'play HDMI monitors, without special software that looks for them. I want to draw the graphics myself, and choose the headset as a second monitor. Does anyone know how a 1280x720 headet would present itself? I am hoping the answer is a single 2560x720 display, because then I can draw everything myself quite easily and any PC video hardware timing glitches for animation will affect both eyes the same at the same time and in the same parts of the frame.

Well, I bought an inexpensive set that was advertised as 1280x720, and even with video chipsets that can do 4K/60, no 2560x720 mode was available, unfortunately (only up to 2K), so resampling is mandatory for side-by-side 3D. Apparently, I am an outlier in eye spacing; I have to use the smallest spacing for the headset to work at all for me, and just barely, as there is no room for any shift without one side getting blurry. Most children couldn't use the set at all. I have a 3D webcam on the way, and it does do 2560x720, but unfortunately, it must be resampled to get to this headset.