[Richard Coutts-Smith]

Rick,
You already have half the snorkel mount, small bracket with 2 holes, 2/3 of the way up the "A" Pillar. The coresponding pins are mounted on the side of the Snorkel, they just slide together after you line them up and let gravity do the rest. (This is the most simple thing about a Humber!)
Pic below (Hopefully it is big enough to show) shows the original air intake reversed, with a two-peice convoluted joiner (From a Volvo Truck I believe). Certainly looks the real deal.
NB. The drivers rear visioin bracket needs to be modified after the Snorkel is fitted, if you want both rear vision and be able to open the door all the way.
Of Historical interest, period footage and articles refer to this apparatus as a "Snork", which always sounds funny to me.
The front bar (See below) is what you need to get if you want to match original, as it has all the stowage gear built in and would be a fair bit of work. Try Russel, even a damaged one will give you most of the information you need to build the entire frame.
It is my belief that the canvas and round frames (In halves) are stowed on the front hood frame, the flat sections on the left side of the truck: remaining pic.
Rich.