GoodParts roller rockers are the only roller rockers you should use on your Triumph, and they're the only ones we use in our shop on the engines we build!  Available in 1.55 and 1.65 ratios, these rockers come fully assembled.
We also offer a mixed ratio setup, with 1.55 ratio arm on the intake valve rocker and 1.65 ratio on the exhaust.  We have used this arrangement on specific forced induction applications, where a little extra help is required on the exhaust side relative to the intake.
Beware!  There are much cheaper orange rockers you can buy on eBay and from other less knowledgeable suppliers, but those orange rockers are not purpose designed for the Triumph six cylinder engine and thus do not fit correctly or offer proper rocker geometry once installed.  The initial savings from the low cost rockers is wasted on hours of effort trying to improve the geometry, factor in the cost of a new hardened rocker shaft, and the seemingly inexpensive rockers are no longer an economical option - especially with regard to compromised fit and performance.