I just measured mine. About 1" a little more in some places, a little less in others. I went with this insulation from Home Depot. Southwest Classics has something similar to dynamat, $75.00 for 25sqft.
Well... Insulation went well, they sell 48" rolls for small jobs about1" thick. Worked great, 3 rolls, $6.00 a roll. Headliner.... Don't expect pictures or help on doing one, you can probably guess how it went. I couldn't get the rear to work right, going to have wrinkles. I think it may have been made wrong. Jean posted about having problems at the rear and they noticed it was stitched wrong. I can't even get the windows back in! Called my glass buddy out, going to cost me some beer.
Is there any way to tell how it's wrong before the install? If you see the problem please share so I can look at mine.
I hear most use the old one as a pattern. Mine has been totally gone for 30 years. This one had lots of overlap in the rear, like the rear window was 4" smaller on each side. Lots at the top, but there was no way it was long enough to reach the inside bottom. The "hooks" the bottom goes into barely attached it. I just split the difference, that's why it has wrinkles. If I would have put it where the top was supposed to be, it didn't hang down enough. Maybe some when I'm rich, I'll have it done again. It'll be good enough for now.