Yes, from what I've read the original CP-1000 upgrade kit was just the lay shaft gears and dog, the two main shaft gears and a first gear shift fork.
I understand that the Trident main shaft is different. AFAIK that's the only difference between the two gearboxes. Except they never were dumb enough to use a leaf spring for indexing the Trident box.
Thanks for the links, I'll have a look. I've dealt with Burton once. The seat on my Trident came from them, good quality and service on that.