
The cylinder liner screws into the body and needs either a rather special pin wrench (its not an ISO or DIN size that I can see), or you can turn down some bolts to the right profile, the holes for the pins are about 3mm diameter as I remember, and hold them in a vice the right distance apart to unscrew the liner. Tapping the group with a large rubber hammer started the liner turning after soaking for a couple of weeks in penetrating oil and sitting in the sun for a while.
The ID of the seal is 62mm, OD 73mm and the thickness today is 3mm. The thread on the liner is non-standard (hardly a shock on these machines), and appears to be something like M63x1.25 although thats not measured with a gauge.
You can see the seal on the top side of the flange in the picture below.

View into the group casting, without the liner in place.




