Tom, Hunley Acuff is the man. This is the only (to my knowledge) true vulcanized process available today. Raw rubber is formed under pressure and heat to the board much like an automobile tire is manufactured.
hunleyacuffrunningboards.com
The Duck's boards are made in China, the rubber pre-cured as with his glue on rubbers. The rubber is then matched up to the board and is vacuum bagged and autoclaved. This is the best non-vulcanized process available, far superior to glue on rubber. The pre-formed rubber is bonded to the board without glue, as it is freshened with tolulene to make the bond. The downside of this process is that any imperfection on the board is magnified on the surface of the rubber. Typically, the welding of the braces on the bottomside produce the sort of imperfection that is visible on the surface of the rubber. Bob is aware of this problem, and may have addressed the issue since I last saw his boards.
http://www.bobdrake.com/
A point of interest here, Vulcanizing, as with injection molding, both require bleed holes to allow the escape of trapped air during the molding process. (See the small bristles on a new tire). A true vulcanized board will have a considerable bump of rubber flow through the holes on the bottom, appearing similar to rivets. Look at an original Ford board to see this, then compare to the Duck boards, and you'll see that his rubber doesn't flow through beyond a tiny paper thin area surrounding the holes, this being a function of the vacuum bag bleeder cloth. Not a problem, but I describe the two for those with inquiring minds.
All in all, the Duck's boards are very good, minus any metal problems, but there's none better than a properly prepared original Ford board sent to Hunley Acuff to be vulcanized as original.