Hummm...unless yours is real dried out/crusty, it stays put and only the cloth covering is replaced. My headliner (cloth part), I think is common, started bubbling & hanging down in places. Got replacement cloth from Kirbans or Poston & an upholstery shop pulled old cloth off (I think they steam it while removing) & I think use a spray glue to put new cloth over the foam. The foam is real dense & pretty much permanently glued to ceiling & would be a huge mess to try scrape it off. Your foam is probably ok, but if real crusty then reckon that's what it will take. Don't know where get new foam, probably Kirbans or Poston, perhaps dealership as they used it in a bzillion cars. Good luck '85GN.