Thanks for that link. Way more car than I have, but it is in the same place! I haven't seen this car/photos. I remember more of a stock application like mine. Oh well.
I have been spending much time tweaking the Banks Dash pad to get it to fit and make it a "modular" assembly. The goal to have the pad, registers, and dash set up as separate assemblies.
Currently I have changed the way the demister vent registers mount to the supports. I removed the aluminum brackets that held the registers into the flange. I formed a fibreglass plate that fills the huge hole by forming the glass over the registers allowing them to sit firmly, and flush with the mounting flange. With the registers mounted separate from the dash top the top will slide over with the vent trim fastened to the dash top, and not to the mounting flange. I extended the flange on the dash top to accept the 1/4x20 chrome screws so it can be held in by the bolts and not have to be connected to the dash board. I also added speed nuts to the outer mounting points so one doesn't have to reach one's hand in behind the dash (potentially damaging wiring, binnacle or glove box) to get a wrench on the nut floating back there.