I have a 67 Plymouth color and trim selector book in front of me, but it doesn't answer all your questions, because these colors were not customer options -- they were automatic depending on what the basic trim color was.
My 67 is DD1 Light Blue Metallic with the H5B-H6B interior -- this is the same blue as yours, without the white. The second color code (H6x) is the carpet, crash pad, steering wheel and headliner color. My carpet is a dark navy color, faded to purple where it gets a lot of light. It is a loop style carpet -- I think it is supposed to be 80/20.
The difference between H5B and H5C is that "B" stands for "blue" and "C" stands for "combination" (with white). The blues used in the combo are the same as the blue used in the B version. Plymouth only had one set of "blue" interior finishes this year for Barracuda: H5 refers to the vinyl color, and H6 refers to everything else.
I think taking in your parts to have them matched would be the most practical solution.