Got it all back together and did a compression test. 2 and 3 cylinders are low. Put a little oil in the pot and tried again, but made next to no difference. Am suspecting head gasket, being that the two cylinders are side by side, and may explain why it was seized up in the first place. Have had suggestions it is valves, but what would be the chances of both going at the same time? Any thoughts before I start pulling it apart? Am going to do a radiator leak test today, just to see if the coolant is going into the cylinders. Would explain it all. As I got no history with this car, I suspect now the head gasket may have gone, and it was just parked up. Over time moisture has got into 2 and 3 cylinders. Sound feasible?