This is a quick test with reverb added. I've "revoiced" the two main 8-foot ranks - really, just rebalancing them in power relative to each other. The "Melodia" rank is more flutey, and it substitutes for Rank 1 of the French harmonium. The "Diapason" rank is a bit more assertive. While it lacks the keen reedy edge of a true Rank 4 in the harmonium, it serves in that role here.
This work starts with both ranks, but towards the end the Diapason drops out leaving the Melodia on its own. There's a fair degree of swell pedalling. The work starts with the swells fully open, and after much variety along the way it ends with them closed.
The French harmonium and its American counterpart were first and foremost instruments of chamber music, though many found their way into churches as a pipe organ substitute. It's with that first use in mind that I've chosen a "medium room" reverb IR.