Going by what the vendor says its an Osgear Super Champion but I have never ever seen one with a toothed jockey wheel before.
The bike is just PUURFECT as it is.
Have a look at the following site for old classic derailleurs.
I am up at Mildenhall for the Bank Holiday Cycle Rally and am doing this on a PDA mobile hope this works.
http://www.hadland.me.uk/