Alastair welcome to the forum. You have come to the right place, I am custodian of the Geo Monro factory records which the VHGMC have. I can date your machine from the serial number, although this may have been lost when engine was changed. In my own collection of literature I have manuals for all models of Monro Tiller and related engines. I am also a volunteer at MERL where the drawings for Geo Monro machines are held and I have been catalogueing these for MERL.