Yep, that ill be a problem to tighten it properly without the lens shroud removed (the notches on the outer edge of the ring are for a spanner wrench; you hold the lens still, tighten the ring, and the vertical force on the threads holds it in place). If you could get it out, though, that points to it not being tightened very well to begin with. Maybe someone has ideas? Medium thread lock?
Using ground glass on the film plane is for checking focus on the taking lens only. You will need to remove the cover on the focus knob and loosen the retaining nut in order to change the infinity focus of the taking lens. To be clear, you set infinity on the taking lens by moving the lens board, then set the viewing lens by screwing it in or out. Anyway, unless you are planning to change the overall/taking lens focus, you don't need to do anything with the film plane.Assume that the taking lens focuses properly.Use the focusing screen and set the viewing lens for infinity focus.