Regarding “Huntsman - Rep Gun” synergy, we talked about it here, so it’s not very useful to repeat ourselves (I just think it’s a strong weapon, definitely an efficient build, but I don’t see synergies with headshots).
About the rest, you said interesting things… but I think Rep Gun is perfect as a weapon, and therefore I would not want it to become excessively strong with hypothetical buffs and therefore to nerf (because you know, when Fatshark nerfes something, they often exaggerate 
)… also because, always in my opinion, if Rup Gun is not a suitable weapon to headshots it’s not primarily for the spread, rather for the nature itself of “spammer”.
The talents you have proposed are good, but here we have (actually Fatshark) to make a decision: to make Huntsman ONLY headshots based (but, then, they have to add more suitable weapons… because, at the moment, only the bow really is… not even Handgun, as it can just bodyshot)… or to leave him an internal niche of “diversity”, more oriented towards spam/bodyshot, and therefore give to him talents dedicated to this…
And, with regard to talents, there would be a book to write… because, personally, I’d revolutionize EVERYTHING. Yes, without a doubt Longshanks is one of those to fix (we could still merge them: + 10% mov speed + no spread reduction moving, for example)… but, speaking of the “not-headshots builds” discourse, the starting point should be tier 20, where we have only headshots based talents (and here, imho, the weakest option is reload speed on headshot… a talent only useful with Handgun… and not so much, since current Handgun relies heavily on bodyshots).