"Jim Blackburn" is the original iteration of the current "Blackburn" you are thinking of. I know the rack may seem spindly, especially with the brake bolt style attachment. But I used that exact model for many miles of fully loaded touring circa 1976-80. Mine was always rock solid with all the gear needed for unsupported touring. I still have two of them, one silver and one black. No cracked welds and no bent tubes.
Charles Hobbs
Fort Morgan Colorado
USA