Thanks for the info all. Now back from the final river trial. Spoke to surveyor re shaft bearing and he said the movement is minor and no action is necessary. The rudder-stock bearing is worn but the vibration is only evident if I lean on the rudder. Yes, it does need sorting but it is nowhere near the end of the world.
Engine ran like a dream with no major smoking (in fact none after a couple of mins) and the oil and temperature remained within the tolerances discussed on this thread. The only problem I did have was with the cold start. The instructions on board say turn key to left (red marker) and hold for thirty seconds and then turn further left (to green marker) to start. After starting the key should be turned all the way to the right (blue marker). For a hot start the key should be turned to the right. Turned the key left to the red marker and the key clicked into place (I did not have to hold it there) but no lights came on. Left it for 30 seconds and then turned further to left and ignition light came on and engine turned over. It took several attempts before the engine started and I wonder therefore if the preheaters are working (or am I doing something wrong)? Hot starting did not present a problem. That was it. Boat handled well and the hull survey is very good. There is also a boat safety until 2018. She badly needs blacking but the vendor has agreed to deduct this from our agreed price, he has also agreed to pay this years license. So, it looks as though we now have a nice old (1978) Peter Nicholls hull. The inside is original and in great condition. The outside is ok but tired paintwork wise. Only other problem is a leaky side hatch but we can sort that. Incidentally, I could not ask the vendor about the cold start as he knows nothing about boats. He inherited this from his dad who has sadly passed. Colin