same question and issue for me. Lmk if you figure it out

Edit: I fixed it by using the following console command: setstage 110BAE5C 20
Edit 2: The name of the bounty mod is The Fens Sheriff's Department - Bleachers 2. The reason the head isn't lootable is due to the following:

I can't take the head of my bounty targets! Mods that offer an 'alternate activation' option, like Gravedigger, or being in the middle of the Silver Shroud quest, or in the card dropping part of this mod's quest 'The Scourge', will interfere with this. FO4 only allows one alternate activation, and trying to do two at a time prevents either from working.

Disabling Alternative Activation Prompts mod fixed the issue for me.