Ford's "Super Duty" name originally applied to the 401, 477 and 534 gas V8's used from the late 50's until the early 80's in heavy-duty applications. I believe they used the firing order you have listed. These engines are physically huge.
One way to ascertain the difference:
Y-blocks (such as the 312) had center valve cover bolts.
SD's had perimeter valve cover bolts.