I have installed liners in the 70 sportsroof and a friends 66 coupe. If both your front and rear glass is out, the job is relatively easy, but time consuming. Proper glue and an abundance of binder clips is my secret. The headliner glue sold by most catalogs (that I am aware of) is too "hot" too many solvents for the headliner fabric and will soften, if not literally dissolve, the fabric. Also, take written notes as to the order of the headliner bows and the particular holes they go into. The bows are color coded with a splash of paint at each end, the holes in the roof line are also color coded. If the color is worn off or painted over, mark the ends with findernail polish - 1 stripe for the first bow, (front), 2 stripes for the second from the front, etc. Use the fingernail polish to mark the hole in the roofline from which the bow was removed. There are 2 or 3 in each spot..
If you search the postings here under my handle and headliner you will come up with a couple posts where I describe extensively the tehnice I have used successfully on the prior jobs. This is not to say there are not other ways that will work, or even work better. This is just what worked for me.
I used short pieces of old windlace ( 2 or 3") for clamps to hold the new headliner in the correct position and after i got it where i wanted i removed one or two and applied glue and replaced the piece of windlace, don't forget the two wires that go on the back rod.