Nice projet Rob.
I haven't seen either of those mods before on Swedish cars. I did, however once have a '53 Oval from Nothern Sweden with double heater channels. These were accessory channels that bolted to the top of the original ones, but still ducted the hot air from the same pipe (under the rear seat).
Maybe Owen will have seen some of these mods before?
47 Beetle, 56 UK Karmann Cabriolet, 56 UK Beetle, 57 UK Type 2, 59 UK Beetle, 66 UK Fastback.