Hey..... I remember you!
I have installed 4 of these. Having the front seat out really helps. Also, when lifting the headliner into place, center the dome light hole in the headliner with the mount in the roof crossmember. Have the bolts ready that retain the shoulder belt of the seat belts. Once the headliner is pressed into place, install the seat belt bolts. These will hold the headliner in place while you install all of the remaining trim parts. Take the seat belt bolts out to slip the seat belt hanger into place, then reinstall the bolt. Do this one side at a time.
The front and rear window rubber gaskets will need to be peeled back with popsicle sticks to lay over the headliner. I used popsicle sticks to keep from scuffing the paint.
Finally, just for kicks, I put padding against the underside of the roof skin as a sound deadener.