You might enjoy the 'King's Lynn Forum' website - free to join (just Google it), there are very knowledgeable people on there and lots of old photos. You could post your questions on there, there's a thread for family history. Did you visit True's Yard museum? There's a lot of the fishing/seafaring history of King's Lynn kept there as far as I know, and one of the people who runs it is on the Forum, he is an expert!
I do agree with you, such a shame the old historic parts of the town were not preserved.
Pat