Will,
In late 1949, the headliner center bow changed from a screw-in style to a floating style. It sounds like you have the earlier style.
To answer your question: the rear headliner panal is put in place and the headliner center bow goes over (under, really) that headliner piece. The bow is oriented to receive the rear of the front headliner piece. The front of the front headliner piece goes under the windshield seal.
If I am wrong with any of the above information, we will hear about it.
Tim
