A high level summary of the Alpine series is here: http://www.sunbeamalpine.org/index.php?categoryid=16
You’ll see the differences summarized – engine, carburetors, axle ratio, negative ground, switch to alternator, etc.. Some of the changes on the series V, such as all synchro gearbox and 7.5" clutch were introduced during the series IV.
You can decode the chassis plate codes here: http://www.sunbeamalpine.org/index.php?categoryid=83
Alpines built for North America were ‘LRX’. ‘LRO’ implies the Alpine was built for somewhere else.