I've attached a series of photos, which help illustrate this rather strange station!
Single line Marsh Mills to Launceston, with various passing loops.

In this photo, you can see the kick-back-siding/headshunt from Coypool and its buffer stops. 5541 is coming from Tavistock, entering the
up platform. You can see the clay branch going off to the right behind the formation.
A shot post closure of the Marsh Mills to Tavistock section, where you can just about see the clayworks in the background. The wagons are sitting on the
down platform line. A loop ran behind the box, with sidings fanning out to serve Hoare Brothers' Tarmac facility.

Happier times, circa 1961, showing a pannier and brake. The box is a replacement for the original Saxby and Farmer example: I believe the original had type 3 fittings, similar to the one at Horrabridge.

This photo, depicting what I believe is the same loco and brake from the previous photo, is looking towards Tavistock Junction. This was the double-track section of the branch before the junction. Tavistock Junction
up yard can be seen through the arches of the bridge, which still carries part of the main Plymouth-Plympton mainroad. A rake of clay empties can be seen coupled to the loco along with, what appears to be a shunter, hanging onto the cab door rail.
I suspect what the photographer has captured in these two photos is a Laira Goods Yard-Coypool trip working, returning light, and then the loco being used to shunt the yard/clay sidings spur as an
as-required move. There was provision for this in the Working Time Table.
Hope this is of some interest.
Best wishes,