I have been researching my father for some time now and he too was a marine aboard the 'Prince of Wales'. My father was also captured by the Japanese and I believe I may be able to help you but before we take this any further may I ask if your grandfathers address was 61 St Leonards Road Prince Rock Plymouth when he joined the Marines. If so, which I'm almost sure I will be pleased to help.
I asked my mom to confirm my grandfather’s address during the war. According to her, when he came home after the war, they lived at 23 Laira Bridge Road, Prince Rock, Plymouth. She is certain, however, that when he first joined the marines, he and my grandmother were still living in Plympton, but she does not recall the exact address. She has a cousin who might know.