manipulating vertical frames

I'm creating a file with 70+ different plainchant antiphons, each one or two lines long. They are numbered and named; e.g., "53. Our Lady of Sorrows - Sept. 15", and at the end of each is "TONE x" designating the psalm tone to be used with it.

I want to be able to align those two labels to the two ends of the staff, left and right. I've tried system text, staff text, rehearsal marks, but all of those are lined up with a note, not the staff itself, and since the notes stretch apart or shrink together to accommodate varying numbers of notes, the first and last notes also move left and right from line to line, and the labels with them. Jo-Jo suggested using "Fine" for the "Tone x" note at the end of the line, and that works fine. But replacing "segno" with text doesn't work for the left side. For some reason, if I select "left align" in the properties for it, it centers the text over the left edge of the staff.

So I'm trying to use frames. Can you suggest the easiest way to do this so I have a block of text aligned to the left edge of the staff and another block of text aligned to the right? And it's over and over again, so if there's a way to fix defaults that would be great, too. I tried using a vertical frame for the left-hand text, but couldn't figure out how to change the outline of the box so that it doesn't extend all the way to the right, bumping the right-hand text to outside the frame.

Help?

Many thanks.