By "Old", just how old are we discussing, here?

And is this a Traditional ballad, dance tune, or Hymn/Gospel song? Any ethnic connections or National origins?

I have a modest collection of music from 1800 - 1930's, much of which is in the form of Hymnals and "Sacred" works. If there is a chance that "Gathering House" fits this genre and period, I might have a look. It does sound a bit familiar, actually.
If I do have it, you're on your own for chords... unless I really like it and it's in a key I can work with.

As you may know, figuring out the foundational melody of some of these old songs from the 4 (usually) part harmony score can be a challange, as they often "skip" all throughout the part-lines, and notes of the melody can hide amidst the tonal nucleus of the chord. I often find myself arranging as I go, until a synthysis emerges that sounds about right on the tin whistle (a commonly available music simplification "plug-in"... ye plugs it in ter yer head!) then hammer out some reasonably compatable chords, and go with it.

If the C. LEVEY Collection is still on line, I would highly reccomend it; it's awesomely massive, and one of my favorite resources for 19th Century Music.