How’s this for a true crime story? A 75-year-old California man was just charged with stabbing and killing a young British couple on his boat off Belize – in 1978. Their bodies, which had been bound and weighted down, were found off a beach there at the time, but the murder trail turned cold until police in Sacramento interviewed the son of Silas Duane Boston recently about the disappearance of Boston’s wife. The son said he witnessed a violent struggle between his father and the Brits on the boat, when the son was only 13. At his hearing Boston, wearing…