The vertical fin is similar to the Mirage 3C. However, there is the addition of an intake at the base used for cooling with the J-79 engine. It is a distinguishing feature of all Kfirs.
Here is the frame
added sides to smooth the surfaces
here is the fin insides
and before gluing
glue on the vertical fin
here is the air scoop
and glue on
lastly, add the brake parachute housing and fairing. Same as the Mirage. I used a wood dowel for the rear dome and painted grey color.
Here is the assembly. Later on the small fairing for the rudder will be added.
Isaac