What year is your 16H, Nick and what trim are you building it to ?
The later-war steel footrests are generally available NOS but up until 1942 or so, Norton used the pre-war style composite rests (which are more rounded and 1/8" shorter than the post-war type fitted to Dommies and singles). The footrest hangers are the same so the early type can be built up using original parts and modern pattern items with rubbers from Geoff Hunter if that's your preferred type. Russells certainly did stock newly-made shouldered stand pivot bolts and the long footrest mounting, but it's only a round bar threaded at each end.
If you're looking for a top level of finish, Ken McIntosh in NZ makes very good cycle parts but of course delivery takes longer.
Most UK jumbles have torque arms....they're not rare, otherwise a Greek seller on eBay will probably offer one again shortly.
You're a lucky man with all those gearboxes...Probably worth as much as a complete 16H if the cases are good !
If you'd like the engines dating / identifying, feel free to message me. I have a particular interest in the pre- and early-war serials and inspection marks :-)