The instructions (page 5) shows the gun magazines, instrument panel etc fitted to the fuselage frame then the engine is fitted, this is the procedure I followed. The engine is quite a tight fit due mainly to the magnetos fitting under the magazine boxes, I had the added issue of having fitted ignition leads to both magnetos. The engine does fit but requires a bit of manipulating, some force is required but not enough to cause any damage to any parts. My ignition leads were bent slightly once the engine was sitting on the engine bearers but they were not damaged. The engineered tolerances are very tight on this kit and all traces of paint have to be removed from any mating surfaces. I had no end of issues trying to fit the bottom wing to the fuselage but once I scrapped off all the paint the wing virtually fell into place. It is great to work with a kit that has parts that fit so well, this is typical of Wingnuts quality.
Don't be afraid to tackle this kit eindecker, you will thoroughly enjoy the build.
Des.