Is it a delta coupling? i.e. that fit's on an a frame shape, rather than straight drawbar?
If so, the likelihood that you have a 1700kg damper is that Bradley now only make these weight variations:
Ergo, the last person to replace it would've gone for the 850-1700kg damper (to cover your 1400kg rating), as the 450-950kg rating one would've been too light.
That's my best guess anyway!
You should be able to compress it (it's the 3500kg ones that take a bit of effort
), I've done a few at that sort of length. Not easy, I have to admit and it'll work your forearms! Also don't slip and smack your hand in to the end of the drawbar, ask me how I know it hurts and I'll show you a good scar on the inside of my palm lol...
If that's not going to work for you then maybe look at cutting down and re-drilling the extension bar that fits to the end of the damper?...