I decided to repair it as described at
http://www.windandwavemodels.com/Repair.html by fabricating a glass fibre splint that is inserted into the two halves of the fuselage. Making the splint 6” long was convenient as I had some 6” wide wing joining glass and this gave 2” into undamaged fuselage each side of the damaged area which I thought would be sufficient to give a strong repair.
The first job was to make a plug to wrap the splint around as using the fuselage itself was not practical due to the extent of the damage. This was made from four 8” lengths of 1” square balsa glued together which was then planed down to the outside diameter of the fuselage as measured at the forward extent of the splint. By using the outside diameter there would be an overlap of the splint which would press against the fuselage both holding the splint in place and giving a better joint. The plug was then tapered over 6” of its length again to the outside diameter of the rear fuselage leaving 2” to be held in the vice as illustrated below.