Yep - resolved to my satisfaction.
It is a wind driven generator mounted on the roof of a De Havilland DH84 Dragon.
Below is a photo from the Ed Coates collection showing both ZK-ADR and ZK-ADS in East Coast Airways markings.
No generators at this point.
ZK-ADR c/n 6090 was first registered with East Coast Airways Ltd of Gisborne and first flew on 25-03-1935.
It was re-registered as ZK-AER to Union Airways Ltd on 01-07-1938 and is seen below (minus spats) with sister DH84 ZK-ADS at Milson about 1939
It was impressed into the RNZAF on 25-10-1939 and became NZ551
It was damaged landing at Rongotai in 1943 and sold to Air Travel (NZ) Ltd.
It was rebuilt by De Havilland at Rongotai and re-registered as ZK-AHT on 25-03-1944.
It crashed on Mount Hope on 30-06-1944.
Below is a link to a seat from this aircraft as seen in a Murchison museum.
Photographs 1 and 3 are from the late R McDonald collection.