I thought i'd give enough time for someone to come on here with some type of solution as how he would make the missing fuselage section but either no one works with fiberglass on here or not sharing for some other reason.
Here is how i did it, i used the former that i pulled out from the back of the fuselage to use as template to make a foam plug!, i found using the foam plug technique would be fastest way to make this section. This is sort of same technique as how my S Connie is made. I used both high density blue foam and low density white foam sheets laminated together to make this plug. Since i was using 2" to 2-1/4" foam sheets in terms of thickness i couldn't cut it out of hand so i used my Delta scroll saw for most of the cutting.
Old former used as template to cut the part.
Cutting the foam on Delta scroll saw
Test fitting the part in the fuselage
When i tested the first part, i was bit surprised to see that one side of the part wasen't fitting properly in the fuselage, for this i had to trim that side a bit. It turned out that for some reason plug or mould was out some what.
Then i kept going with cutting the other parts out to make the whole plug.
I also had to fench the last foam piece to make it fit into the exhaust nozzles, otherwise it wasen't possible to plug to fit and lock in the fuselage.
Once this plug was half done, i realized that it has to the sanded down to match the taper curve of the fuselage going in to tailcone section as know as aircraft exhaust nozzles. So i hand sanded the whole this to match the shape and this took a while as i had to do it in sections a bit while fitting the plug into the fuselage and taking it out to match the curve.
All sanded into the shape.
After main body of the plug was sanded into the shape needed i secured the parts with 2 long 1/4" dowel to enhance to lock so there would no movement of the plug inside the fuse. This was important to do!.