The circuit in message 15 works - it is the circuit of the Tele 787 modified to remove the coinbox elements. Bell only added if needed.
I've just set it up as per the circuit in Msge 15 with a Tele 713 and a Jack Unit 1B - luckily I had some Tele 713s and Jack Units 1B in the 'Stores'
. And it worked first time.
Dialling tone loud and clear on lifting the handset.
Replaced handset and dialled into the circuit the Tele 713/Jack Unit1B was fitted to and it rang out until I lifted the T713's handset and was able to speak between the two phones.