Looks like a suitable candidate kit for British Oak type hoppers can be kit bashed from the Knightwing Models mine top buildings (PM113) as detailed in the weathering for railway modellers vol 2 book by George Dent - will need to crack on and order one - another option could be sourced from one of the Walthers coal mine kits - as based down-under so will ned to wait for the COVID interfered with shipment.
The Knightwing Models kit has just arrived - on cursory examination it will probably suffice, once enlarged with some additional Wills panels, to suit an On14 module structure based on Paul's plan suitably antipodeanised - already have one of Mark Clark's Steamnthings Barclay E class locos too shift the coal hoppers, to be based on the Snailbeach ones.