Disassembling the dash on a 54 is not for the faint of heart. When originally assembled, the upper die cast half was put in place, then the instrument cluster was installed and lastly the lower die cast shell with the various controls and switches installed was put in place. Many years ago I attended a UAW luncheon of retired KF employees and met a guy whose job it was to fit the dash and he said it took two people to do the driver's side installation.
Access to the heater controls is best done by removing the lower half. There are several nuts/bolts that need removed - one where the under dash light is positioned near the driver side kick panel (unfortunately this end of the dash is broken off in the photo) and another where the lower half meets the rest of the dash - you can see that nut/bolt in the picture, as well as another just above it - in the photo it's above and to the left. There are several phillips head screws to remove, it sounds like you've done that, and a couple of bolts securing the lower panel to the steering column as well.
Once loose, the lower half won't drop very far since all of the wiring will be stiff from age and won't want to move.
Best of luck!
