I have decided to take the easy way out for the gundeck... Ran planks straight off and trimmed where necessary. None of the edges of this gundeck will be directly visible on the completed model.
On the top deck I will put down a margin plank and 'joggle' the deck planks into this... (Wonderful hobby - learning new words every day... :) )
Composite image showing completed gun deck - started scraping the deck - still need to sand and seal. darker verneers ('caulking') will stand out more at that stage. Total time logged on model to date - 47 hr of which 33 hr spent on deck planking and using the walnut veneer as caulking.