Help with identification, please

[symbolen]

Hi!
I have a Kubota L185 with an two-stroke motor. My problem is that I don´t know the enginenumber. Can someone help me please?

 

[RDR]

Z751 743cc's

 

[symbolen]

Z751 743cc's

Thank you!
The say that it is built 1981. I don´t know if it is true??