Can you scale focus?
For night focusing with the rb67 (with which scale focusing is a bit difficult*), I have put a flashlight at the point of focus, aimed toward the camera. That works well enough but of course it isn't always practical.
*Note to interested rb/rz users: there is only one lens for the rb/rz line with which you can do easy helicoidal scale focusing, namely the 100-200 zoom. For all others you have to scale focus via the bellows factor chart on the side of the camera, which is a minor drawback.