They are much larger than a soft shelled clam. It takes about 4 years to mature. They are found on the East Coast, mainly between New Jersey and Cape Cod. They are used mainly for chowder and for being stuffed. If you can' t find quahogs where you are, you can substitute using the largest clams you can find, the flavor and texture will be a little different.
Stuffed quahogs are time consuming to make and that is why they are made in large batches.
You do need an old fashioned hand grinder for this recipe. A food processor just won't do. But, all the work is worth the effort. Also, linquica and chourica are both Portuguese sausages that are spicy. The chourica is very hot and spicy.