Alan,
Yes, from the factory. Using a straight line as a plane, the carb-mounting area was machined down (at the front) approximately 25 degrees. When the boat accelarated, the carb would be at a near level angle. Unfortunately, some guys tried to use these manifolds on the street. Well at idle, the front intake runner tubes would load-up. If you didn't keep the revs up, it fouled-up the front cylinders. Also, imagine driving with one of those things, and then hitting the brakes. Mucho gasoline rushing forward. Thats why they said, Marine Applications Only. Some of the early 66' manifolds (that were bored to 1 11/16" or had the center shut-out removed) did not have the carb-mounting area angle-milled. These
could be utilized for the street, and D-Dart applications. Of course, I have no idea of the part#. Somehwere in the basement of my fathers old shop in Peekskill, NY there probably sits one, from Viking Boatyard

Paul