The stuff at Harbor Sales all seems to be rigid or semi-rigid, it might work but it isn't what's on the I28. The I28 overhead liner is a sandwich of old foam rubber padding (now degrading into dust) and soft vinyl, with many large access zippers (often disintegrating pot metal pulls) and millions of staples under a heavy rubber trim bead to old it all up.
Clearing it is best down with a respirator because of the foam turning into dust. And in theory if it was removed carefully, you could laminate new foam onto the vinyl, install new zippers, and put it all back up. Except, the zillion staples and inevitable distortion in the vinyl could make it a real "Old Enlgish Sports Car Restoration Project". So to speak.
Talking to a friend about the same job, same boat, at length, and we figured either trash all the old liner, and replace it with some type of flexible high-density foam (like gym matt padding) or gut it all and install traditional lattice boards running fore-and-aft, across stringers running athwartships, either bright varnished or painted white, and allow some ventilation that way while avoiding the huge upholstery project.
That also ensures no invisible leaks behind the overhead, and about a million less staples in odd places, and balky zippers.<G>