There was one here in South Florida back in the late 90's. 68 Charger, slant 6 and 3 peed manual. The owner was in or Chrysler club at the time. He gave me a ride in it.
Ran pretty good with a slant 6. He dumped the clutch and did a few burnouts. I also agree that there probably were more than 2 or 3 built in 68. Never saw another 68 Charger with slant 6 ever again.