OK, thanks for your help. Do you know of a machine shop Beds/Herts/Cambs based who has experience of doing the job ?

Thanks again
Simon

Have you tried the new luego owners, cos the old ones had the tool to do it and I believe they might might have bought the tool as part of the business. Worth a try.

I'll give the Luego chaps a call. I missed a trick here, I thought that the Sierra upright was used un-modified.

Thanks
Simon