This afternoon I have been drilling three 8.5mm holes in some 12 mm plate that was very kindly cut into bits 9.5cm by 6cm by a fellow triumph owner to make spacer / mounting plates so that I can use a Land Rover Discovery mount type NRC2053. The centre hole had to be tapped 10m so that the mount could be attached and once screwed in the extra length of the mounting thread was cut off. The other two holes are positioned so that they will accept the original fixing bolts.
The Land Rover mounts are not very expensive but as yet I do not know how well they will last.