According to Smith/Creek, pg 87 in their book, the rear firing 20mm cannons were only fitted to the V21 prototype.
As well as V-19 a four engine B model that was designated the first C model prototype
For a very long time now I have been trying to get a copy of this book.
It is a rare book & copies are hard to find. At last I have got one for my self.
All the aircraft that were captured & were able to be flown by the allies came out of Norway.
This book also supports the no rear guns except for the prototypes. As I listed before in this thread only the C model was ever fitted with rear guns. It lists each aircraft that was there in Norway & lists those that was deemed possible to fly for the Allies.
It also breaks down who flew what aircraft back to their respective sides for example Eric Brown.
He only flew two.
Now just to refresh the memories of some,this is what the firing ports & ejection shell chutes would have looked like if they had of put rear guns on the B model.
These images are all C models.
So lets look at the two Brown flew.
#140581 This was a reconnaissance aircraft it flew with 1.(F)/33 a recon squadron it had cameras & those are located in the compartment the rear guns would have been if installed.
Photo of that plane.
#140356 This aircraft was in II./KG 76.
This was a bomb squadron no cameras here so the rear area for guns is empty & has a possibility to be a rear gunned AR-234B?
No there is no gun ports on it.