Wow - I got custom 1920x812 60hz and 23 hz and 3D working with Mojave settings. That's pretty cool.
I could never get 3D to work previously if I created a custom 23hz resolution. Maybe NVidia have changed something (or madshi madvr?) because before you definitely couldn't get 3d to work if you had a custom resolution set with a 23hz refresh rate.
I did notice however that the projector still goes to 1920x1080 24 (23.976) when in 3D mode but hey with Mojave settings in madVR it still works just fine. (I'm pretty sure the projector wouldn't accept a weird resolution for 3D anyway)
I have set default desktop res to 1920x812 60hz and changed MC settings>Tree View>Full screen to 1920x812 60hz so everything now fits the screen ratio. After a 2d or 3d film is finished it goes back to 1920x812.
Oh I've also turned on custom resolutions in MC under settings>video>Display Settings and set the default desktop res of 1920x812.
PS. Ive also been able to turn off the theatre view 13% overscan border and now the whole of theatre view fits in the 2.40:1 ratio..