I have now bought a banjo centre to go with the side pieces acquired earlier.It is in very good condition with the 6 off threads at each side and the 6 off threads for the nose piece all in good condition. There is no square plate at the back, just a threaded hole which may be 1/8 BSP. There is a drain plug hole but no hole for a breather tube in the top.
The stamped in markings are a bit faint but the date appears to be 27/7/27 and the raised portion at the back seems to have 5321/ 9 44 stamped in although this will mean nothing if I rebuild it with parts from my existing D axle.
This will be a winter project if I keep the car.
My wife and me are starting to suffer from old age and arthritus which can make it difficult to get in and out and for me to avoid her when changing gear so I have been hanging my nose over Austin 10s but we'll have to see.