Hi Mario,and a big warm welcome to the forum.
There should be a small brass plate attached to the mower frame that will give you the model and mower serial number.
Bonmow was part of the Scott Bonnar range in the late 50's and early 60's and made in Adelaide.
I have never seen one the same as your machine, but from the pic I would guess that it's a 14" model with a Villiers motor.
I will try and do some research for you.
