The only other time I filed this was ten years ago. I have no idea where I filed it - wherever the instructions said to.
Below is a link to the instructions for Form 709 for the last 20+ years.
https://apps.irs.gov/app/picklist/list/priorFormPublication.html?resultsPerPage=200&sortColumn=sortOrder&indexOfFirstRow=0&criteria=formNumber&value=709&isDescending=false
Great. Thanks so much @Anonymous_ . Only 1 place to send it; seems they could figure it out themselves.