Speedbrake cutout
When you make the speedbrake cutout in the bottom of the fuselage, be carfeful about the location of the cut that you make for the rear of the cutout.
If you use the approach of putting masking tape around the scribed lines, and then cutting just inside the masking tape, then you will actually be cutting on the scribe line, not inside it. For the rear edge of the speedbrake, you might want to ensure that you cut just inside the line instead. This is because the scribed rear edge is exactly below where the front edge of F4a is - so if you cut on the scribed line like I did, you end up cutting away the Aeropoxy fillet - that's how close F4a is to the speedbrake.
This can be seen in the attached photo.