Putnam Beckwith was the son of Zera(h) Percival Beckwith, and grandson of Samuel Beckwith and Lydia Gridley. My ancestor, Sylvester Gridley Beckwith, was Zerah's brother. He moved to IA, was killed in the Civil War, and the family lost contact with the other relatives.
Check the Ancestry.com website, get to the Beckwith genealogy forum. There is a query about the Marshall County Beckwiths. Perhaps the person placing that query may be able to help.
There are a few researchers of this line, but I have had little or no coatact for about 10 years. One is Carol Daun Croft who published a Beckwith History and a Croft History (Euphemia Beckwith was sister of Zera and Sylvester, she married Hutchison Croft). Another is Jane Lockwood. But I no longer have current addresses.
Check the Ancestry.com Beckwith forum......Mahlon Erickson