Hi anyone know anything about locking diffs and the options ? can they be retrofitted if so whats involved ?

There are normally two main types:

ARB Locker (activated using an on-board compressor) - ARB don't make a locker for the L322
Detroit Lockers (self contained unit that detects with grip is lost and automatically locks the diff) - I can't find one of these for the L322 either.
Detroit TruTrak (limited slip diff) - again, not found one available for the L322.

So, unless you can find a way of fitting P38 diffs into an L322 then you're stuck with the HDC.  

The l322 came with a front and centre locking diff as standard triggered by the dsc or tr iirc.

An active rear diff was an option on some models iirc but I don't see why one couldn't be sourced and retrofitted and activated in the ecu like its been done on d3/4's a few times now  FFRR MY06 facelift With TDV8 Alloys Zeros/ATR's
Mantec Sump Guard, Rigid Load liner, MY10 BT upgrade.