New or old hightower?
If the new version, beware, I had a nightmare getting the correct size dropper post – you have to be aware that although the seat tube may be long enough, the position of the shock means that you might not be able to push the post all the way ‘bottomed out’.
The cable/hose has to route around the shock (i.e. off centre) and then into the seat post.
On some posts the cable is central (like a reverb) on some (Fox transfer, Brand X) its off to one side slightly and on mine, interfered with the bottom of the seat tube and shock at full insertion.
Just beware that there may be some trial and error involved.
Of course the beauty of the One-up is that you can slide the whole lot up 10mm and then shim the travel down a touch – I nearly ended up doing that myself.