Removing setting the entry widths to fixed numbers of characters seems ok (commit 1).
But I do not like the look of the other two, having labels above the entry is different to every other dialog in Geany and every other replace dialog in editors I have on this machine. I also don't like the removal of the close button which allows me to change my mind.
Also I am not sure its right since it seems to no longer set a parent and that may modify the dialog behaviour (platform and desktop dependent).