Hi, to complete the original call for help, which was answered admirably, thank you - the engine is now back up and running.
I was able to polish out some light scoring of the journal and replaced the bearings using plastigauge to check the clearance which was 3 thou with 6 thou shims fitted both sides.
I torqued up the nuts to 90nm which was what I calculated was their setting when I removed them. I needed an extra small movement to get the holes lined up for the split pins.
The whitworth spanners ( wrenches) and sockets i brought were very useful.
I was able to double check the oil dip stick settings and it was good just at the bottom of the caps with the dippers totally immersed.
The whole sump was cleaned out as was the strainer and the magnet at the end of it ( nothing on it ) I primed the oil pump and checked it operation on running
The biggest challenge was knowledge, confidence and confined space.... the latter manageable despite being in the small engine room on my canal boat.
I now have the confidence to clean out the sump at the required hours ( albeit necessitated draining 10 litres of coolant, removing the starter, alternator and water pump. All no doubt meat and drink to you engineers out there but for this novice a challenge of recording everything and taking a lot of time to double check everything.
Pleasingly the engine fired first turn of the key and settled with not noise to its normal tick over which I let run for the first hour. We then did a small cruise keeping the revs to tick over most of the time.
A huge thanks to all who gave concise common sense advice and guidance and have stayed with me over my ( extended) learning for this work. I feel I know so much more about my engine thanks to your support and encouragement. Sincere thanks, virtual pints all around - sorry warm brown English beer I'm afraid !!