Retaining Wall Questions

[Crazy Dazz]

Ok, bit of a strange one for Ford forums, but I recall we have some stone-masons here...

Looking at a block of land to purchase...

The block is 30m deep, and overall drops away from street level. So we'd be looking to retain along the back (11m) and along the sides towards the back. That is now the normal practise here, but this is in an old part of the suburb.

Overall I would estimate that the existing block drops 1~1.5m from street to back fence so adding 1m of retaining should be plenty.

HOWEVER, the back fence is onto a commercial property (their carpark) which has already been levelled, and so it is already retained. Using that precast modular concrete ("wonderwall").

So my question is how can I "add" to the existing retaining?
Can I place "L" blocks on top of the existing retaining?