I'm probably preaching to the choir here, but have you tried getting a death certificate for Marion from surrounding counties? Is it possible he died somewhere else? Do you know where he's buried? Cemetery records no help either? I think many county clerks will give out birth information only for births prior to 110 years ago. BUt thne he may have been born before records were kept in Decatur County.
If you can get somehow back into the 1800s there's a good chance we have some ancestors in common as the Bivins (Bivens, Bivens) were pretty prolific in the New York and upper New England area before the "kids" started moving west and south. Lots of branches to explore.
I'll look in my stuff and see if any of your names correspond to any of the "extra" Bivins I've found in census indexes.