These days, the VoIP adaptor configured as a ringdown circuit is probably the cheapest and easiest way of doing it. If you want to build your own
https://www.vintage-radio.net/forum/...9&d=1485945957
Not completely sure, but I think you have a missing regulator board in your 706. It plugged into the ABCDE contacts.
Refer
http://www.samhallas.co.uk/repositor.../0000/N806.pdf
which suggests that the phone should work de-regulated if BCD are connected together.
You also appear to be missing your bellmotors. Bell unmounted 59B ?