Ken,


This is very atypical for current MVVS engines.

Since I open and check each and every engine that I sell, before giving/sending it to the customer, I can tell you that I have not encountered any such slag on the inside of any engine.

Any harmful foreign matter (aluminium particles?) is equally rare.
Sometimes there is some congealed oil, or fibrous matter, from the cloth/paper used to wipe the engine after machining.

As Jim wrote, it should be less of a bother to disassemble and carefully clean away those imperfections, just be careful not to scratch what should remain smooth (for sealing), or you may void the warranty.
It should take you about half an hour, including disassembly/reassembly.