Series 3 had leaf springs, the 90 marked the start of coil-sprung Landies.
Well it marked the start of the SWB coilers and they were actually called the "Ninety".
The "OneTen" was the very first of the traditional shaped coil sprung Land Rovers, in the early 1980s ('82 or '83 or thereabouts), it was approximately another year before the Ninety appeared. Even then, the Series 3 (leaf sprung model) continued for another year or so alongside the new variant.
The 90 and 110 designations didn't start until the "Defender" models for the '91 model year, so late 1990. This saw the introduction of the 200Tdi into the Land Rover, which had already been in use in the Discovery.
Lots of LR History sites, here is just one:
http://www.lr-mad.co.uk/
