Like said above, the closest it came to passenger cars was the Jeep Cheerokee trucks.
As far as headers, no one I know of has made a specific header for the port shape the Magnum heads have. In fact, like normal, typical aftermarket companies just use the old X,J etc.... port shape on what ever header is being made for what ever use on the header design.
The most important part of the header is the top half of the pipe that meets the head. The bottom portion is not as important. I have this issue as well with the Edelbrock heads. The bottom of the port is not like the X head.