Thanks very much indeed for all the input. One of the links indicated that the spigot could be Loctited into position, so that is interesting.
I was a bit surprised at KWIL stating that it was not easy to silver solder cast iron. Not knowing that, I have always been able to silver solder to CI without any problems. I suspect my success is no more to do with me, than it is down to the flux used. My father was a welder and sheet metal worker. I inherited the flux from him and I believe it is / was a BOC product. He always took me to task silver soldering to cast iron, but that was because Sif bronzing was much cheaper!
I will try and work out how to attach pictures, I always fall foul of too high a resolution and I can't remember the free resizing programme that I used to use.
Everyone seems to indicate that I would be better off junking the cast iron chunk. Now wait a minute…….. I seem to remember Prof Chaddock remarking in his Quorn book that "it was cast steel and it cut like free cutting mild steel, which in fact it is". Just checked on that and found my memory is correct! So big apologies all around for the duff information.
Thanks everyone for the assistance so far,
Andrew.