The wide chisel brush I bought is much too wide! What was I thinking or imagining??
The glue-stiffened organza will work, I think. And I experimented with the lettering, tracing a couple of letters to fill in with marker and with paint. The marker is too faint and the paint is the winner despite being more difficult to do. Luckily I have a narrower brush and will just have to suck it up and manage the lettering as best I can.
The B on the right is the marker on the organza. The one on the left is on the paper towel underneath. The U on the right is in paint. As you can see, the paint is the way to go.