Rob, I am also researching Alexander Marsh for my sister who is K. Marsh of Plymouth, MA. My nephew had gotten back to Edmund Marsh of Duxbury and stopped because there was conflicting info. I concluded that there could not be 2 Edmund Marshes from Duxbury, born on the same day, married to the same woman, and died the same day, but the middle initial was different. So I traced Edmund S. Marsh back to Alexander Marsh
of Braintree and am now trying to figure out where to go from here. Have you been able to glean any info to date.