Do you think I would be able to reinstall the original headliner in my 67, or would it rip from age? Its in excellent condition,no rips.

It will more than likely tear. Remember, the material is 40 years old and has been subjected to the temps outside.

What do you have to lose? If it come out of the car?? I think it will fit.
have even got away with it from one car to the other on a hot day
The crease is already there to hang the sides and front
Be careful and follow along with the welt trim shut the doors and get her hot
A day or two takes most of the wrinkles out

I think the threading will rip...

You could get s sewing machine and restitch it...or do it by hand...