Just an update to this thread.
Investigated the strange grinding noise - turned out to be a well knackered main bearing. Strange thing is - it seems Lizzie is a bit of a weird one. The main bearing on the side that drove the compressor was a split type. The chap I spoke to at stationary engine parts had never come across one like this.
Anyhow, managed to modify a standard bearing to fit into the split casing.
Then she got cooked. My fault - the cooling system was airlocked and I didnt spot it in time. Exhaust valve seat was in pretty poor state after that - zero compression. A quick regrind and she's running again, but I'll need to fit a new seat next time the head is off.
As of this moment though, she is powering the plant cooking up a batch, my dishwasher, laptop, TV and lights.
You could say that this message has been posted by Lister power.