Pz IV and III turrets look similar but don't have the same dimensions. The Pz IV turret is wider at the front and, as a result, the taper angles to the sides and rear are different as well vs. the III turret. The turret ring diameter on the Pz III was smaller than that of the IV...which is why the III was ultimately rendered obsolete while the IV was able to be up-gunned.
I've got 1/35 plans for the J and L, let me scan those in for you.