Early 273 intake problems

The new aluminum intake has an angular raised boss shown in post 1 - picture 1 - holes #4 and #6.

You may have later model heads. OR if your heads have the older casting numbers, they could have been machined to the new specifications [manifold bolt holes being square to the intake surface]. These were the early years for the LA motors, and who knows what happened to your car in the last 55 years. If Chrysler had ordered say 10,000 heads with the old casting number and had a bunch leftover, would they trash them or machine them to the newer specs? And give them the new part number.