The Heron pictured in Georgano is a 1925 model with a front-mounted Coventry-Simplex engine. This still had a plywood, chassis-less body, but the engine and gearbox were mounted in a subframe and was easily removable from the car. It carried a 'proper' radiator (probably by Serck) which bought it in line slightly more with the other Westcar products.
Having dug a little deeper into the story, I think this probably is a Westcar rather than a Heron; the Westcar Colonial model had a 12hp Dorman engine, but the Heron was slightly smaller and had a Ruby engine of 8hp. Also, the Westcar Colonial didn't have any doors (no doubt due to the flimsy nature of the plywood construction), having steps for entry, like the puzzle picture. The Heron (and, I think, the Marks-Moir) did have doors. If the puzzle car is said to have a 12hp engine, then it is probably a Westcar, but it should be listed as a Westcar Colonial model.
According to Mike Worthington-Williams, the bodies for both were built by Samuel E Saunders Ltd of Cowes, Isle of Wight, who later became part of Saunders-Roe, building plywood aircraft bodies. The Heron/Westcar bodies were delivered by boat to Southampton docks and then by Lorry to the Westcar works in Herne Bay.
The Colonial model appeared at the April, 1924, British Empire Exhibition at Wembly, and the smaller Heron was first seen at the October, 1924 Olympia show. The 'other' Heron, the front-engined version, was shown at the Olympia show in October, 1925, after which the marque stopped exhibiting and had been wound up completely by the middle of 1926. No more than 100 of all were built, and probably nearer to 50. I think there are a couple of surviving 'Strode' model Westcars, but no Colonials or Herons...
