I am sure that the grill logo on a 1968 cabinet would say Kustom by Ross.
Basically Kustom starting putting serial numbers on speaker cabinets starting approx October 1969.
Kustom by Ross speaker cabinet production ended sometime around that time period, so it is possible that October 1969 is when Kustom Electronics speaker cabinets started.
Kustom by Ross speaker cabinets were made well after Ross amp heads production had ended.
Timeline
Ross amp heads production - 1966 to May 1968
Kustom by Ross speaker cabinets - 1966 to October 1969
Kustom Electronics speaker cabinets - November 1969 to December 1973