RE: Rebuild....but different
The fin size is difficult to guesstimate
On many so called aerobatic models -- the modeler would often make the rudder and fin larger-- to make th thing "knife edge better .
but strangely they did not improve .
If you tip the model on it's side - you see that the percentage of side area ( lifting area ) AFT the cg is now much further aft . this will as the model transitions from level to knife - automaticaly , allow/ cause the nose to drop.
On the best , latest aerobatic stuf for slow speeds - the entire side are is greatly increased , with only enough rudder /fin to allow easily controlled pitch and yaw during knife or upright flying.
these models roll with minimal inputs and tho some may doubt it --they are incredibly stable in all axis - with no dihedral
The models look odd to those used to traditional layouts but they are far better aerobatic performers.