[quote=Popping off the head to measure the bore and stroke might be the only definite way of working that out!
[/quote]
Okay I have done that. It has a 2-1/2" bore exactly, meaning it is the right size for a VK-40. I didn't measure the stroke. But I doubt if this is a VK-40 because the exhaust and intake ports are the wrong way around. I wonder if it could be an American engine block, such as a LAV-40? That would explain the reversal of the ports.
Incidentally, the VK-30 bore seems to be 1-1/4", exactly quarter inch less than the VK-40.
Thank you also for the info about the Gregorys books.