Base models that didn't cover the B or C pillar posts are held in just as the early Bugs. You still have metal rods used as bows to support the headliner in 3 or 4 places but the edges have strips of fibreboard swen and glued to the headliner edges. This then pops over the metal lip of the roofs inner support channels.Looking great .
Did you do the headlining yet ?
If so please post pics as I need to pick ideas from it , as I have no idea how a base headlining fits in