Here are the few parts that make the AB exhaust assembly
in my opinion, the designer could have done better by having a much deeper and longer duct.
Here it is with the rear fuselage sections.
So I added another cylinder to the duct to make it deeper. That also required internal modifications to the frames to accommodate the longer duct.
In order to preserve the round shape of the AB duct, I used Yoav's method of inserting a dummy frame and then applying Super Glue ( CA ) around the perimeter to stiffen the cylinder. After 10 minutes, the dummy frame is removed.
note,
I can insert the AB duct from the rear without gluing until the end, so you may see it in and out at various upcoming pictures.
Dry fit first
Isaac