George is correct on the primaries. The exhaust pipes are actually 60mm (2.362"); tail pipes (tips) are 70mm (2.75").
Wilkinson also sold (as a set) stainless steel headers and mufflers. These were also available in mild steel. Primaries are 45mm (1.77"); exhaust pipes are 60mm (2.362"); tail pipes (tips) are 3".
I don't know what he is currently selling.