Sure, I have a suggestion - how about gray perlon?
I ran around for a number of years in what I call my '72 "R" with no interior at all. I finally wanted to quiet it down a bit (without changing its personna all that much), so I installed an Ap Biz RS carpet kit and a gray perlon headliner. I bought the material at a local fabric store. They had a number of weights, so I chose the heaviest. This is kind of what the original R's all had, except I believe they used red. I think later RSR's did this as well.
I made a cardboard template before cutting any felt. I made it big enough to go well into the channels on the front and sides, above the doors and windshield, so I could tuck the edges behind all of that. I used 3M aerosol headliner adhesive for the headliner rather than the the DAP tonneau cover contact cement used on the carpeting. I found the spray on adhesive easier to use for this, and it seems to hold plenty well enough to hold the felt up there.
Two sets of hands are essential. Mark a centerline front and rear on both the headliner itself and on the windshield and rear window. Work from the center out so you don't trap any air. Use a really stiff plastic squeegee to "sweep" it down (up?) into place. This is a "compound" contour, so as you work out from center it will want to "pooch" out or fold over on itself. The material I found was stretchy enough to work those out and, since I was tucking the edges out of sight on three sides anyway, it didn't really matter if they wound up a bit misshapen as I stretched and worked it down.
I left the rear roof vent rain tray uncovered. I noticed it is just a crudely folded up three sided piece of flat sheet stock. As such, the vertical seams between the front edge and the two sides will leak. I'm not sure how the factory sealed these seams, probably with headliner glue, but I just used silicon RTV. Otherwise your nifty new headliner will get wet in the rain.
That's about it. It's pretty straight forward.
