I realize that you had made changes to the antenna and that looks good, within what can be done with 3-D printing. I doubt that 3-D printing can ever get as fine a mesh on the reflector as PE can.
But, the directors you have paired with the Mk 4 antenna shows the extension boxes on the back associated with the Mk 12/22 pair of radars.
Here are two images of the back of the Square-Back Mk 37 director with the Mk 4 radar antenna installed. Also, note the worker standing behind the antenna and note the relative size of the antenna. The first image shows a very early version of the Mk 4 antenna. The second image shows a later version Mk 4 antenna in 1943.
The image below shows the back view of a Square-Back Mk 37 Director with the Mk 12/22 pair of antennas installed. The extension boxes can be seen.
Thank you for your very informative comments about the differences between various Mk 37 director antennas.
In a message posted some weeks ago, you already mentioned that the Mk 4 and Mk 12/22 were different, so we made corrections to the antennas of the kits produced by Black Cat Models.
I will post very soon photos of the two antennas types, as I do not remember if I have sent to Steve the set with the Mk 12/22 antennas.