I think I remember that old magazine as well- article about small grain elevators. Photos of wood boxcars with temporary grain doors still in use in use in the late 1960s (70s?) at some little elevator somewhere... no idea which magazine or when.
My attempts at web searches came up mostly with conveyors that look like coal conveyors, and various sizes of front end loaders.
- try a search for 'vacuum grain loader' or 'truck mounted vacuum grain loader' - this turned up a bunch of photos for me, but appear to be current production machines.
Not sure if that's what you are looking for. Looks not unlike a cyclone dust collector, with several pipes and hoses attached.
Here's the company that claims to have invented the vacuum system. If you scroll down, there's a photo of one circa 1970s- not truck mounted, but I suppose it could be.
https://walinga.com/assets/client_files/files/downloads/brochures-pdfs/WalCorpBrochure_WEB.pdfHere's a whole page of grain augers (how it was done in the old days), but again, from your description, I don't think this is what you are looking for.
https://stock.adobe.com/search?k=old+grain+auger