John, the buttcap is brass, but is plain (no scrollwork).
The end of the tang is just peened over the buttcap. There is no keeper, diamond shape or otherwise.
And, I am pleased to say there is a scabbard, although the chape and any sort of frog (if there ever was one) is missing.
I will email you some pics of the handle and scabbard if you want to see.
--Mike L.