Just to add, might help others, I have just put a new headliner in, bought off eBay uk, £180 including postage. It a GRP replacement with a single layer AGD/Oatmeal on the front, I folded it in half and went through the rear doors, the colour was good, texture and feel looked reasonably good, but, it had no sound deadening material/heat insulation on the roof side, which I was disappointed with. I rang the supplier and he wanted another £15 for 3mm foam backing, it was the weekend and I was ready to get going, couldn’t wait. So I used the original Jaguar backing layer minus the old front material. It was a tight fit, and just went in behind the new GRP panel. It was a struggle round the security centre pillar top sensors and I probably should have trimmed 1/2” off the sides of the Jaguar backing panel to allow the new one to line up on the front and back window edge’s better.

it was a pain, so if you are concerned about road noise or heat loss in winter and keeping cool in summer(UK weather) and don’t want to struggle with the Jaguar backing pad then make sure you get it added on or add it to the back yourself. One good point the supplier suggested to me was wear cotton gloves to move the headliner around in the car. Also clean the top of the front seats, because if they are dirty they will mark the new headliner, as it rests on them, when you are moving it around to get it into position. Did have the option of buying the material and spray on glue, but was concerned about quality of fabric and bending the jag backing pad so opted for the GRP.

 

I am in the same situation and also live in Southern CA. I need a new headliner and installation on my Vanden Plas
Anyone? Bueller? Bueller

 

My R didn't have any insulator between headliner and roof. Therefore it was really tinny. When I replaced mine I installed two long stripes of thin sound dedning plates(dynamat etc) covering almost all of the roof area.It is now so much better and no tinny at all.