For many people with the old transmissions, a slowly moving propeller is a fact of life, and many don't really consider this an issue. Naturally, if you want the prop to stop you can turn off the motor, and with the old fashioned big chrome lever we used to see in boats, you could always tug back slightly and achieve perfect stability because those transmissions had the ability to "slip the clutch". Here is a photo of the big chrome lever on my 17' Sportsman boats (1956 and 1957, this is the 56)
Naturally, if you are using the boat frequently and need close quarters manuverability, you'll want to "do it right" and get those Paragon bands adjusted properly. If you are doing mostly cruising with limited close quarter manuvering, you could adapt your driving style and run the boat for years just as it is, as I suspect the previous owner did.
Regards, Paul