Here is a simple script for creating a horizontal rule over a text frame: https://wiki.scribus.net/canvas/Horizontal_Rule_over_Text_Frame
The idea is to select a text frame, run the script, which asks for the length of the line as a percentage of the width of the text frame. A 1.0 point line is created, centered vertically and horizontally over the frame, after which you can adjust the vertical position and other properties of the line as desired. Greg
