I had to buy a second hand defroster duct for under the drivers side, and replace the ducting to both as well. It isn't that difficult or strenuous, just need a little brute strength. I used the newer rubber type, looks good.
I'd recommend flattening the duct end before fixing to the duct, the length that Clarks supply it at is just about perfect for both sides.
I also found that my heater blower worked today, and that it didn't work through the switch. I wired directly to a power source and went throught the switch to the fan supply,so that at least it looks stock. My thermistor has fallen apart, it is only mounted on card, and it had just gotten too brittle. I've ordered a new one, hopefully it will make it all work again.
Unfortunately the feed I wired the new feed too had a 10 amp fuse in, and that blew, so can I presume that it is safe to just keep upping the fuse size until it keeps working? Does anyone know what fuse should be in the heater fan feed?
I haven't seen a good description of picture of the fuse box in a 64 vert, and I have even bought one of those coloured wiring diagrams from ebay. if anyone has one or can point me at one then I'd appreciate it.