I'm going to guess it's from the factory. Mild steel wires were commonly used to suspend and hold the cores in place when casting the block. These wires were "almost" always removed by the foundry before machining the block.

Last edited by DavidBraley; 08/05/2021 1:38 AM. Reason: Spelling
-David

1953 2-Ton GMC

I'm a machinist... because engineers need heroes too.