Looked up Silas Johnson in pension index and best I can do for you is eliminate a few

Silas Johnson of Co B, 21st Ind Infantry whcih became 1st Ind. Heavy Artillery Rgt died about 1911 his widow was Elvia

Silas of Co. C, 140th Ind. Infantry died in 1912

Silas of Co. K, 50th Ind Infantry--his widow was Sarah

Silas of Co. K, 57th Ind., Co. B, 134 & Co. B, 147th Ind. Infantry Regiments--his widow was Julia