Unusual Engine Number

[RUNNERBUN]

Here in Australia, most of our engine numbers are prefixed with a CA followed by the numeric and a star at each end. I have just been given this A engine (*CAU8511*) but the number is somewhat unusual (to me anyhow) It is prefixed with CAU, This is the first I've seen with a CAU prefix. Does any one know what the significance of the U is.
I also have two other early engine blocks which have the 5 bearing cam shaft, one which has a four digit engine number in the mid 4000 and another in the 15000 range. The Four digits in this CAU motor falls between these two early engines but it is not a 5 Cam bearing motor.
Unfortunately this engine has some serious corrosion problems and may never see the light of day again.
Thank you in advance for any information