The source I used is D9020/48, which is a German manual from WW2.
Its title, translated, is : “The radio equipment in Sturmgeschutz Ausf.G”
Illustration “1” is titled “Installing the Fu 5 and Fu 2”.
It shows how to connect and place the radio sets, the power transformers, the antennas, the loudspeaker and the intercom.
According to various German sources, a typical Stug might have only the Fu 5. A platoon leader would usually need the Fu 2 as well. But the allocation of radio gear would depend on what was available. The vehicle had enough radio holder frames that you could put either radio set on either side, to suit the crew’s preferences (e.g. the commander could operate the radio, or delegate that to the loader).
Illustration “2” is titled “Installing the radio sets Fu 8 and Fu 5”. That is relevant to unit commanders only.
The manual has other diagrams showing how to wire up the intercom, how to install the “star” antenna, etc. It’s a good read if you are building a Stug.
You said that you “checked with the RFM kit”. I don’t recommend using RFM as a reference - they make great efforts but they get many things wrong.
Use photos of real vehicles, and manuals where possible. Museum vehicles are often missing a lot of items, but in the case of the Stug, there are some great examples around.
In this case : RFM give you the Fu 8 and Fu 5 radio sets in their Stugs. As I mentioned above, that layout is for unit commanders only.
Now, the Fu 8 requires the “star” antenna but RFM do NOT give you that. So their kit is incorrect out of the box, whether you apply unit commander decals or not.
You wondered if the radios themselves are accurate. That is not a problem. Both of the companies mentioned have quite accurate radio set boxes, since the Fu 5 and Fu 8 are well known, with many photos on the Web.
Finally : you tell me that I’m confusing the Ausf.E with the Ausf.G. But really, I am not confused on that point. I’ve also read D 963/9 which is the radio manual for the Ausf.E.
The fact remains that this Border kit gives you two complete Fu 5.
While it’s physically possible to install them both in the vehicle as depicted, the German organisational structure for armoured units doesn’t make them both useful at the same time. Platoon and company commanders would listen for orders from above but they were not supposed to talk back. Whether a Panzer or a Stug, they were supposed to carry a receiver for that purpose without a transmitter. That’s a single box and it’s called the Fu 2.
David