I do have a stuart cat with pics of this engine, did not realise the air pumps were in fact petrol pumps but did think they looked familiar.
They were made by AC Delco if you google AC petrol pumps it should bring web sites such as Cornwall Austin 7 restorers with cut away diagrams as to how they work.
Also Rimmer Bros who do overhaul kits. They were fitted to many cars espec ially Ford Cortinas Capris Escorts (rear wheel drive).
You should be able to pick up a pair at an Autojumble overhaul is simple with the kit just diaphgam and valves.
If you can build a Swan no problem.
You may need to mod the rocker arm that drives them but should be no problem. On cars it was driven by an ecentric on the cam shaft.
Good luck JK