The design of the Three-Seated Destroyer is based on the Special Hobby Saab AJ37 Viggen kit in 1:48 scale. (No, I did not pay the price listed there, but it would be worth it, it is an excellent kit.)
I have used only a few parts of the kit, basically the front part of the fuselage, the forewings, and the exhaust nozzle. In addition to that a lot of polystyrene sheets, a piece of mold runner (pole) and lots of body putty went into the model.
I have trimmed off the jet intakes and covered the holes with PS sheets, changed the scale from 1:48 to 1:144, cut out an outer airlock hatch (not visible), and inserted a deck plate in the place of the original cockpit. The cannon is made from a piece of PS pole that is carefully centered in the nose cone.
In the picture, you can see the deck floor of the three-seated cockpit and the opening of the inner airlock door.