William, I run a 'One Name Study' on all these names, so have large volumes of records from around the world. You are correct in the assumption about James William coming from Maine. I have him in census records back to 1860. For 1850, I believe him to be the William TABBUT age 14 living in Addison, Washington Co, ME with David LOOK and family. Unfortunately this does not help define his parents as he is shown as a pauper; I guess his parents were probably dead.
The spelling is mostly TABBUT or TABBUTT and this is an extensive family in the Columbia and Addison Townships of Washington Co. I can trace this whole family back Joseph & Elizabeth TABBUT who went to that area in 1755. They were from England and their eldest son was born in England in about 1748.
I have trees for all the parts of this family and have looked to see if there is an obvious space for James William. There is no certain link, though there is a John TABBUTT marrying a Lydia ROBINSON in 1829 for whom I can find no subsequent records.
Mail me direct on firstname.lastname@example.org if you want more infomation.