Thanks BDA and Brian - I did wonder if that tube would stop air getting to the dash vents. Thanks for the tip about motorcycle fans too, eBay is awash with them at reasonable prices, so looks like a plan for the rebuild.
Made more progress today, deployed the angry spanner on some of the nuts and bolts that would not undo and removed the radiator, air horns, blower, and (just using a socket!) the chin spoiler. Having to jack up the car and remove the n/s front wheel to attack the air horn fixings revealed just how much is going to need doing once I get to the Meccano phase, but I also noticed how much the light shines through the body tub, like a magic lantern. Is this standard added lightness, or has some coating fallen off?