AFAIK Opera stores such settings in '~/.opera/opera6.ini'. That file contains a '[Windows]' section and in it a 'Browser Window=...' entry. This entry seems to contain: x-coordinate (of the top left corner), y-coordinate (of the top left corner), width, height, and state (0=normal, 1=minimized, 2=maximized). Both coordinates, the width and height are obviously given in pixels.
EDIT: I'm sorry, it seems to be another case where I've read the question posted only half ... Anyway to include the "-geometry WxH+x+y" paramter to the 'wbar' config one could use something like:
sudo sed -i '/^c:.*\/opera /s#$# -geometry 700x500+50+50#' /usr/local/tce.icons && wbar.sh
Please note that the re-start of 'wbar' (via 'wbar.sh') is required for the change to be picked up.