how do you tighten the top nut when instead a hex hole the adjustment **** is there? to clarify, i mean that when i try to tighten the top nut, the whole shaft spins with it. on the OEM setup, i just used an allen wrench and a 14mm open end wrench, and now there's no spot for the allen wrench.

 

If you notice at the top, in the threaded part of the shaft, there are two flat sections with no thread. Grap a pair of pliers, clamp it on there to prevent the shaft from twisting and tighten the top nut.