Hopefully you've bought some good donuts, there are a lot of bad ones around and if they split the failing drive shaft can do a lot of damage!
The advice on the Triumph forums is not to use the pattern versions even though it's very tempting to do so. On the Rimmer Bros site, genuine donuts are £186 each rather than £33 for the pattern! That's why Canley do a CV joint replacement shaft (very expensive!) and various people have engineered their own. Apart from any other considerations it's much less prone to vibration.
Some (like the Canley conversion) use the original hub and bearing.
http://www.tengaston.plus.com/Vitds1.htm
Others adopt the Rover 100/MGF bearing and hub
http://www.gt6.ca/josh/cv_rotoflex.html