Ben
The regular series 2's and 3's can be stacked 2 high, the reason for the Lightweight's design was in fact something unique to the Brits.
In the 1950's the RAF carried series 1 Land Rovers side by side in one of their freight aircraft (Bristol 170 Freighter I believe), when the series 2 came out the extra couple of inches in width on the new Land Rovers prevented them fitting the 2 rows inside the aircraft. The solution was to develop a series 2 variant with the same body width as the series 1.
http://www.adf-serials.com/nz-serial...RF_NZ5906a.jpg
Diana
Addit:The aircraft may have been the Blackburn B101 Beverley (a version of the General Aircraft GAL.60 built in the UK)
http://www.beverley-association.org....-r/XB261-e.jpg
P.S. the aircraft type may be wrong but the reason correct.

