Very interesting...a mystery for sure. It wouldn't be the first time someone mistook the copper pre-plating for brass. I've never heard of a 60's brass Supra without a welded seam, but there's a first for everything. Also, a COB Keystone badge shell with a serial number would be exceptionally rare. Does it have crimped beds? The edge of metal at the bearing edge flange should fold back toward the shell if it's brass.
The seller wrote to me asking the same things, I gave him the same response. It's really tough to tell without seeing it in person. He might need to do a shaving at one of the lug holes to know for sure.