Hi Graeme,
The SD1 air filter box that you have was fitted to UK market cars running SU carburettors. I don't know if NZ received these cars directly, Australia certainly did not. The SD1 models imported through Leyland Australia for the Australian market were fitted with Zenith Stromberg carburettors and separate rectangular air boxes. The SU carburettors could not achieve the tightened Australian ADR rules in terms of acceptable emissions.
Any of the large inlet air boxes found in Australia arrived most likely via private imports. The only reason for the large inlet on the SD1 was to accommodate the adjustable cool or hot air intake which heavily reduced airflow reaching the engine (see photo). As a means of improving the airflow to overcome this impediment, the size of the inlet was substantially increased. The photos below illustrates the set up for SD1 models sold in Australia from 1978 till 1981 prior to the introduction of fuel injection. Range Rovers continued with Zenith Stromberg carburettors for a few more years. The P6 models continued to be sold new in Australia until 1978 when the SD1 arrived.
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Ron.
