My observations of A65 engines and the stamping would suggest the engine was stamped A65 12345, A50 12346, at the first juncture.
The second lot of stampings would be the model code and Date/Year code.
I am thinking the frame was stamped with the complete number at this point as well.
ie A65LA7041Y or DC 20846 A65T

Why, Y, Dash Y..