Thanks much Doc Drew. Back to your 25x micrograph, there is the appearance that the body of the darker etching material and the body of the lighter material are fairly uniform. The grain seems to have the appearance of significant heat affect where the forge weld joins the two.

Looking forward to the article. Hope you etched that Ithaca Crass defect. I'd guess that was at a major weld failure, a manufacturing defect, rather than a material inclusion.