I pulled this from the internet. Not sure if it correct or not. Maybe someone else can verify:
That would be a 6 cylinder 1957 Dodge engine block.
K: 1957
D; Dodge
S: Standard
6: whatchagot
16432: 15,432nd 6-banger cast (beginning with 1001)
Actually, the S stands for DeSoto. The 1957 DeSoto Firesweep used Dodge's 325-cid V8 and the engine number prefix on the 1957 325 engine was KDS - 1957 Dodge DeSoto.
When the 1957 model year began, the Dodge six cylinder engine number prefix was D72. But on January 11, 1957, the engine number prefix was changed to KDS6 at number 9601 when DeSoto began building six cylinder Firesweep 4dr sedans for the taxi market. The Firesweep six was not much of a success - total production hit 139 units.