You know if you can guess down to fractions such as that then it is not going to make a hill of beans differance in flying. Actually an inch or so either way will not be a problem. Slightly longer will of course move the CG aft slightly but nothing you can,t handle with placement of other components. But if anything the slightly longer will improve on pitch stability.

So just go ahead and make your guess and build a new aft fuselage with box section fuses thats usually pretty easy to do. I would recommend that since you need so much of the aft section that you not try to splice any remains of the fuse at the tail. Instead build the aft fuse from tail post to the rear wing saddle area. just strip off any portions of the fuse from the tail feathers and install then on the newly repaired fuse just as it they were an arf.


John