Wikepedia, the online encylopedia, has an excellent reference page for the Pajero.
Engine and body variants are described with dates, photos and specs for each generation from Gen 1 in 1981 right through to the current Gen 4.
(Its worth noting that the majority of Pajeros currently offered for sale in the UK are Gen 2).
Highly recommended reading http://en.wikipedia.org/wiki/Mitsubishi_Pajero


