Calling F1 Experts: Who Autographed This 1960′s Shirt?

A friend of mine recently came up with this shirt.  Through some research, he believes that it could be from the 1967 USGP @ Watkins Glen, though that is just a guess.  The names that can be identified are:

  • Graham Hill
  • Dan Gurney
  • Denny Hulme
  • Mike Spence
  • Jim Clark
  • Michael Parkes
  • ?
  • ?
  • ?

The question for you, is: Who else autographed this shirt?  Can anybody confirm which race it was from?