Hi. I can't possibly be the only one having another nightmare trying to fit the C post covers as supplied
by Newton Commercial with the headlining. I think I'm going to have to pull off the cloth cover around the edges
and reshape the board. Does this sound familiar? First nightmare was the headlining but done now

The cover goes under the rear and side window seals, and needs to go in before the parcel shelf "cover".

For me the board was too thick to be installed, I cut it up quite a bit to try and fix it. Sounds like the same problem you are having. I ended up giving up and installing the original ones.

68 + 86auto. Exactly that, card too thick. I'm going to trim the edges and then glue the fabric under the rubbers.

I have just finished doing the hoodlining, windows and C-pillars from Newton.

I also had to peel off the vinyl and trim a long, thin slice off the front edge of the cardboard so that it followed the contour of the frame where the rear quarter window catch mounts.
And don't trim the hoodlining until the rubber window seals are fitted!