I just figured out how to do this, and I figured I'd pass it on. Also, it might be
helpful to put these in the default pdaXrom tosa.xmodmap unless there are
reasons not to, that I do not yet know about.
Anyway, I decided it would be easy to remember, mapping the square brackets
to the (printed) angle bracket keys. And the curly braces to the (printed) parentheses
keys. These would take effect when both FN and SHIFT modifiers were pressed.
SO, edit /etc/X11/kb/tosa.xmodmap and change the four lines as follows:
keycode 20 = l L parenleft
keycode 71 = comma semicolon parenright
keycode 72 = period colon less less
keycode 36 = Return Return greater greater
keycode 20 = l L parenleft braceleft
keycode 71 = comma semicolon parenright braceright
keycode 72 = period colon less bracketleft
keycode 36 = Return Return greater bracketright
I hope this is of some help to some folks,