You are probably only going to get a decent compromise between dropping smoothly and falling in a level attitude. I'm pretty sure that even a full scale torpedo will drop nose down if it falls far enough. It will partly depend on how well the fins stabilize the torpedo. It also depends on the weight of the torpedo itself. A very light torpedo ie.an empty cardboard tube, might turn into an unstable lifting body if the CG is far enough aft and the dropping airplane is flying fast enough. A torpedo with an aft CG is also going to be less stable, wobbling as it falls. You don't mention your intended drop height. If it isn't going to fall very far, the wobble and thus the CG becomes less critical. The best advice I can give is to make up four or five disposable cardboard tubes with different CG's, maybe even as far back as 50% or more, weight them to match your intended scale torpedo and see how they drop.