I am sure that you will all be pleased to hear that my drive problems are resolved! The pulleys were looked at VERY carefully and I noticed a wear groove that matched the "tail" of the inner most links. Checked the groove section and noted 40 degrees inclusive. Fenner suggest 34 degrees for pulley diameters under 118 mm diameter (which both link belt pulleys are). I put both pulleys up in a friends 15 inch Harrison and re-machined the grooves to 34 degrees. Belt now sits lower in the groove.
The link belt appeared relatively new but was highly contaminated with oil. I stripped off every individual link (50) washed in Swarfega Heavy Duty Degreaser, then in Hot water and washing powder, finally in1.1.1 Trichloroethane. Reassembled belt. Re-fitted pulleys and belt and noted Keiths comments about tension, it is now B tight. Refitted motor with new std V belt, aligned.
Originally a .75mm cut on 50 mm diameter free cutting Mild Steel would slow the part down to a crawl. Now a 3mm cut (6mm off diameter) hardly changes the speed. Swarf is not blue so still some way to go
Main reason IMHO is the included angle change to 34 degrees, the belt is now sitting deeper in the groove.
Many thanks to Keith for his comments on Tension. I actually checked a neighbors Boxford. He has the older Canvas and Rubber type belt so did not help a lot. If I had a Boxford I would definately look after the belt, a change to the modern Nu-T-Link could give problems as it is certainly not as flexible. Damn Boxford is definately quieter than the Viceroy though! However bet it would not take a 3mm cut!