Ok well I went for it today and took the lower part of the leg off, followed by the power head. No problems with removing the 6 powerhead bolts. It was all very easy really.
There was a fair bit of salt and sand but no total blockages. I didn't remove the cylinder head. I cleaned out most of the salt and then reassembled the power head and reverse flushed through the tell tale using a steam cleaner. Worked a treat. Unfortunately I do need a new power head gasket before I can do it back up permanently. The existing one came right apart when I pulled the head off.
Having seen the inside of this little engine I would say that just regularly reverse flushing though the tell tale, perhaps with salt away, is all it should need.
Cheers for all your advice, she'll give 20 more years service I reckon