Here is an attempt to put this issue to bed. IMHO, there is no question that the case of the 3717 is steel - not aluminum. This is based on conversations with a certain materials expert with a lot of experience with steel, aluminum and other materials used in the aviation industry. . Beyond that, the weight is consistent with the gen based on my running over to an AD and trying it on having worn the rep on the way over - seriously. So I cannot attest that the weight is exact but there would be a big difference if a significant portion of the watch were aluminum. Aluminum is a lot lighter. Second factoid, Aluminum does not allow for the same level of polish as stainless and when you do get it to a highly polished form it will show every scratch. Although there is a finite amount of polished surface on the watch try the polished ring on the case back.
If you still are not convinced feel free to try this test. Screw off the case back and either apply a dremel or put it on a grinding wheel briefly (the inner surface please as I don't want any "I ruined my watch and it is all your fault!" ). The sparks on high quality stainless steel will be a bright white. Lesser steel should send of a yellow color. Aluminum will not send off any sparks.
And no a magnet is not helpful. Ever tried to stick a refrigerator magnet on a high quality SS refrigerator?