The exhaust cone and rear of the jet engine should have the same diameter. If gluing the flaps in the lowered position, you can see the step. Note: No need to correct if gluing flaps in up position.
Cut 2 pieces of K & S .5625" OD (outer diameter) brass tubing .47" long.
Cut 2 pieces of Evergreen 3/8" OD styrene tubing .15" long. The inside of tubing should taper to inner edge. Outside edge .325" ID (inner diameter), inner edge .375" ID.
Tack superglue .47" long brass tubing to KH parts C45 (exhaust cones). You want to have the cones and brass tubing symmetrical around the edge. Apply super thin Cyano glue on inside of tubing/cone join.
Place KH parts C35 and C50 into C45. Slip styrene tubing into cone opening, making sure not to go in too far and interfere with C35. Glue styrene tube in cone opening. Remove C35 and C50. Fill seam gap with super glue.
Sand exhaust cone flush to brass tubing and to inner diameter of styrene tube opening. Use photos of full size Banshee for shape reference.
The forward side of the brass tubing can be sanded and blended after gluing onto KH engine parts C39, C44 and C47, C48.
I put 220 grit sandpaper on .5" tubing and sanded the area around the engine exhausts for clearance for the engines. Tape keeps tips of wings from getting sanded.