If you are using a curing brine (one with sodium nitrite), I use to make a similar sausage, called Taylor Ham (aka New Jersey Taylor Ham); but instead of using cure pork butt, that recipe calls for using belly bacon. For that recipe you only added the amount of cure for the green uncured meat weight. For example if you are using 7lbs. of uncured butt, and 3lbs. of cured butt, you will need 10.5oz. of cure (approximately 1 3/4 teaspoons), for the 7lbs. of uncured meat.