I have to revise and clarify what I posted above.
From actual Chevy parts manuals and the "Catalog of Chevy Truck ID Numbers", the DB suffix was used for the '58-'61 passenger car 283 with powerglide and 4 bbl. carb. That suffix doesn't show up again until '65, where it designated a 2 bbl. 283 backed by a 4-speed used in the Chevelle/El Camino. DB continued thru '67 for the Chevelle/Camino 283, and in '68 designated the 2 bbl. 307 used in the Chevelle/Camino.
Regardless, with the DB being used for the 307 for one year only, chances are good it's a 283.
