The frisket works! I went to the hardware store and bought my best guess at a new bolt and suddenly the Arab is getting frisky with the frisket. It just looks like it belongs there, swinging from edge of the platen, and so far in my brief experiments, it appears to do the job which I need it to. Some fine tuning from one of the helpful amateur engineers in my life might help it to work better, as the way it's sitting right now is going make printing paper more slow and fiddly than it should be. But at least slow and fiddly printing is better than inevitable inky paper jams.
Another happy printing development yesterday was the discovery that I can print vinyl stickers i.e. bumper stickers. A friend suggested making 'Addicted to Capitalism' bumper stickers and my mind ran off with the other possibilities afforded by printing sturdy waterproof labels. Experiments involving both white and transparent sticky-backed vinyl are extremely encouraging.