Headliner now, count your bows are they all the same size? If your car had a dome light now is the time to take measurements it will save you time after the headliner is in place. I use a heavy cord and made a loop and lightly taped to the back side of the headliner, if and when I wanted to install the dome light. Just make a slit where the dome light sit and then pull your wires through.
I decided to not use the Dynamat the weight vs adhesive they used, I didn’t feel comfortable with, didn’t want if to drop down and rest on the bows. Went with the tried and true method of using the felt and can spray adhesive. If you cannot find the correct felt for your car, I have used polyester before, local Wal-Mart carries it, used in making blankets and such.
Nice job should be a looker when you get finished….