Curiosity got the better of me! Found the link...
http://www.scribd.com/doc/48540023/G...nsion-Steering
This is an invaluable bit of info for anybody working on Triumph chassis, steering and suspension. Anybody who finds it useful should download the PDF because you never know when these sources may disappear.
The castor settings are near the bottom of the document. Briefly you shim the bottom wishbone front or rear as appropriate to adjust the castor, but need to keep an eye on the camber at the same time.
PS. This link also takes you to other Triumph data.