I cut out bulkhead 18 19 and 20 and started laying out an opening for the engine. The engine rails will extend past 20 but I am not sure how far so i just have extra material sticking out. A lot of things are happening between 19 and 20. the engine gets mounted and all three flying stabs need pivot points built into that area. The engine needs to be as low as possible to make room for the flying vertical stab pivot. Using a single engine in the bomb bay area leaves plenty of room for the flying horizontal stab pivots.