[Brian]

Yeah, I struck that soft graphite sorta stuff in an inlet port of a C69A block I was porting; it just kept going....I ditched that block. I'd never encountered it before, just thought it was some imperfection in the iron. I, [probably incorrectly], formed the opinion since then, that the post war blocks were cast of an inferior grade of iron to the pre war offerings, because I'd never struck this before. I do know the later blocks don't weld as nicely as the early ones....Interesting that you've found it in a 99 block, generally considered to be one of the 'better' blox.