The box outside Culbowie Lodge seems like a private post-box, belonging to the Lodge. It may have an old Collection Plate inserted or even a made-up one. I don't know, but you've seen it so you know best.  https://osm.mathmos.net/postboxes/box-info/?ref=FK8+158     Fact is according to the post office that Ref No. does not belong here. (look at the link). 