The major difference is length. Trophy shocks vary by about a quarter of an inch (off the top of my head). Not a big deal by itself, but the linkage is a 4:1 ratio so that slight longer or shorter can add up to a bit of difference in the overall height of the bikes rear. 327mm comes to mind, the answers are here on the forum.
If you put your bike on the center stand you can get a good measurement of the eye to eye length, then compare to the one that's available.
Last note: I would not buy a used Triumph shock, they are crap and generally are shagged by 20K miles. Better to spend your coin on the Hagon. Well worth the money.