916 and 996 cases are totally different. stud spacing is different because of the 98mm pistons instead of the 94mm pistons of the 916 motor. 916 barrels will not fit the studs or in the cases and vice versa, stud spacing and the outer diameter of the barrels are bigger on the 996. sps cases are different from standard 996 cases, they are deep sump which i believe you need a special exhaust to clear the sump. pictures would help cranks are different between 916 and 996. the spline for the stator are different so you cant swap them as the 3 phase staot wont work in a single phase cover and vice versa. stroke is the same though.