Got my Henchel turret in for my Taigen King Tiger* with the Porsche turret and I'm happy to report its a very easy swap! First remove the Porsche turret then you'll see the ring that is attached to the hull, this is secured by 4 pins into 4 holes with some glue, possibly the Crazy type but I can't swear to it. Pop the ring off by prying it up with small flathead screw drivers toward the INSIDE of the ring so you don't scratch the hull. Once you get the ring popped off take your Henchel turret and install it onto the hull, TA DA! You just swapped your Porsche turret to a Henchel turret on your King Tiger!
* DISCLAIMER; My King Tiger is a Taigen, however its upper hull has the Heng Long brand stamp and a part number starting with HL underneath of it on the inside so I must conclude this swap will work for all Porsche turret Heng Long and Taigen King Tigers. I can not say for certain as to Torro or Tamiya King Tigers as I have never even seen them in person. If anyone knows for sure as to the other brand King Tigers I would go off what they say.