Kent 711M BA "XXXX" and "XX" Block,Chasing History and specs

I Picked up a Kent 711m BA engine the other day (AUS) but it has some different markings (to me) cast into the block,an internet search only nets snippets of information and the reliability of the info is so so.These inlcude 4 "X" castings on the hot side along with large 65 numbers and two smaller "x" castings on the cold side inbetween the engine mount threads.I have pictures to upload but I do believe there are Restrictions on URLS ...Now to the point,Whats the history of these engines?Do they have different bore wall thicknesses as people seems to say?Any information would be greatly appreciated.

The four X  and 65 Castings

Two smaller X castings.

I saw one sold on the UK based Ebay and it was quoted as being a "race block" although I have to question this as were is the hard information to back up such a claim?

Could it relate to South African cast blocks?  They made them up until a few years ago over there

These blocks have a slightly higher nickel content.
 
Some have the add on casting behind the rear alternator mount.
 
When core shift has been controlled these blocks will go 85mm.
 
Have sonic tested heaps of them and there is a massive core shift issue with 3 and 4 in about 25% of them. 

http://www.thekentlives.com/index.php/tech/engine/castingnumbers/