The adapter is for the factory stock. I just made sure that my CZ and the stock were never in the same location at the same time until I could get them separated. Not sure how much the ATF cares about such things, but it is better to be safe than sorry.
I don't think you could put a Tailhook on a Zhukov stock without some major surgery.
The Tailhook's ATF letter references the previous brace ruling recently clarified by the ATF. While the newest clarification letter doesn't mention GHW by name, it is much more likely that it falls under the same rules as the SB Tactical. This whole situation is such a mess, you have to decide if that's good enough for you.
Having had the Tailhook for the better part of a week, I think it's pulling away from the SBT Evo as my preferrred solution. Pretty happy with how it works. I shortened the LOP on my adapter to 12.25", and I found that the brace functionality was improved significantly. I also like how it tucks in when shouldered. This is really a phenomenal solution. At this point I don't think there's much advantage to the functionality of an SBR over the versatility of keeping it a braced pistol.
William
