We don't have synonyms for sowbelly yet — it may be a rare, specialized, newly coined, or misspelled word. The closest thesaurus entries we have are soberly, potbelly and somberly.
"The process consists of laying a side of bacon, profanely called "sowbelly," flat on the ground, and eliminating, by a dexterous use of the knife... — Collections of the Kansas State Historical Society (1918)"
"The process consists of laying a side of bacon, profanely called "sowbelly," flat on the ground, and eliminating, by a dexterous use of the knife... — Collections of the Kansas State Historical Society (1918)"