Marty,
https://www.curtain-tracks.com/6018-met ... rrier.html
https://www.recmar.com/6018-metal-block ... heels.html
Here is what I found in a 4 minute search on the Internet. Check and see if the measurements match. I am sure that you can find other sources as well.
I applaud your fathers desire to fix and help maintain older church buildings. My parents, along with the members of their ward, built their local church building. That's how it was done.
Our FMG manager said that if there are any issues with the black background curtains on the stage they will just remove them. I don't know if this is a local interpretation or more wide spread. Might be something for your high council rep over facilities to have a friendly off the record discussion with the FMG Manager to get his input and advice. That way you can head off putting in a FIR having the unattended consequence of someone removing the curtains completely.