Thanks Michael ....
Somehow I got it into my head that using the backside is 'cheating' but on reflection that may not be so.
The Bergger paper that the carbon printers are using is not Cot-320. There was a discussion of this recently on the Carbon Mailing list... One of the printers from Europe is getting paper 'custom', the Bergger PN42 Glossy and Pn 41 half matted.... without the silver added to the emulsion, just the gelatine coating.... I think the cost for this worked out to about 5 euros per square metre, and has the advantage that you can order in small batches.
I had not connected the Cot-320 with the Bergger silver supreme.... So I think it may be possible to get the smooth Bergger papers without any coating without purchasing large volume... Makes me think they may be a better source than Kodak... if the Cot-320 is compatible perhaps the other Bergger papers are..... I will try the backside of some of the smooth Bergger (I have the J&C I think this is the same as Bergger) this weekend and see how it prints. If I get a reasonable print I will contact Bergger about purchasing small amounts of the smooth uncoated.