Estes USS Enterprise #1275, Part 24, Forming & Gluing The Rectangles

The rectangles are flat, the tube is round.

On the left, notice the right and left sides don't contact the tube.

On the right is a much better fit.

Curve the rectangles by pressure forming them around a dowel or around the Sharpie barrel shown here. 

The picture on the right shows the slight curvature

The intercoolers and rectangles are glued on the engines.

All are centered on their pencil lines at 7/32" from the rear of the tube.