Both my blocks were imports & yes, the numbers were stamped one at a time, they are quite crooked!

Unlike most other A series which built here from the mid 60s, all Cooper S motors were imported fully assembled.

You could buy a new S short motor also, which I nearly did in 1968. (but I got an 1100S one instead, it was $100 cheaper).
All BMC's short motors came with no numbers, you had to get a Police number allocated and stamped on. I did this, twice... in 1966 and 1968.

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DrMini- 1970 wasaMatic 1360, Mk1S crank, 86.6HP (ATW) =~125 @ crank, 45 Dellorto (38 chokes), RE282 sprint cam, 1.5 rockers, 11.0:1 C/R.

A little off topic but,

is there any correlation with UK mini block numbering and Aussie... let us say in the cooper S as the dc said all imported.... i ask because i saw a reasonably common practice in UK for a rebuilt motor to be shaved and remarked with new different stampings coded and recorded (record files kept of the entire build) , i uttered amazement at possibly wiping away the value of a 9FSay block .?

Oz Cooper S motors came from UK with an aluminium tag engine number rivetted onto the block.
BMC removed it here and stamped the number into the block. The tag was often then left tied onto the front of the motor.

In UK they just use this tag, there is no number stamped into the block when new. But, us convicts being villains need a permanent number stamped.

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DrMini- 1970 wasaMatic 1360, Mk1S crank, 86.6HP (ATW) =~125 @ crank, 45 Dellorto (38 chokes), RE282 sprint cam, 1.5 rockers, 11.0:1 C/R.