Finally found this one and although the spindle has a Myford nose thread so would take my chucks, the bore was for some obscure collets. The alternative to trying to find such collets was to make a new spindle, bored MT2 so that I could use my Myford collets. Here is the result.

BTW re the hole in the top (with the pointer) I can only think the reason for it is for an extension arm to take a tailstock centre, the hole does not go through onto the spindle so is not for a lock screw. If anyone knows what it is for I would be glad to hear.
Mark