Just about everything can be found with some time and money..I have converted both my 67 and 68 to heater delete...The vent box can be found on e-bay from time to time and is not cheap for a good one.The early ones open like a stock heater.The 67/68 boxes are different .Early boxes are side open door and 67/68's hinge at the top.The fire wall plate is available repo for $25.00..I do have a few(oem) spares.The dash plate shows up quite often on e-bay and isn't to much money..Fire wall plugs can be a pain to find.I believe the correct ones are plastic not rubber.I think air con cars used plastic as well.Not positive if the rubber plugs for the engine fittings are correct but they show up on e-bay (C4 part number).I have NOS ones here..You will have to deal with the firewall pad.
I do have a early vent box but it opens right to left not left to right (
?)I have sold off all my other early stuff...Picture is about half the stuff I collected.Correct box for your car are the two on the left.The 2nd from the right has the reverse door.
Cory