Jacko didn't express herself quite the same way Stevie does, but she had (if memory serves me) the same sort of 'fits' (though much smaller, because I think she would be hit or smacked if she 'resisted' by the junkies who had her). She would tensely offer her head for a scratch almost like a defensive offering. Kind of like 'well if they pet my head they won't grab me'.
Michael said most of what I would've suggested.
Empowering Stevie while still protecting yourself is the way to go.
I think, if the metaphor helps, that I would compare him to a human being who has had their boundaries violated a lot---sometimes in the end they end up being the sort of person who won't say no even though on the inside they're not comfortable---and occasionally they 'have enough' and try to stand up for themselves. Or (I have complex PTSD so I'm familiar with this) they have moments where they're triggered from the past and react. I'd also maybe compare him a bit to a child who has attachment issues---they still crave attention and love but they're a bit disorganized and afraid etc because of parental abuse/inconsistencies or maltreatment.
SO with that in mind, again, empower him (don't assume just because he lets you do something that he wants you do), and show him the world is safe, secure and will respect him.
Three things I did with Jacko that I found really helped was a) what amounts to attachment parenting (she ate, slept, bathed and was near me as much as feasible) b) I let her come to me (for example if she wanted petting I would place my hand like a foot away from her and offer a scratch---she had the power to choose to walk to me or not but I'd never reach for her even if she appeared to want it) and c) blanket sessions where I'd gently cuddle, pet and massage her under a blanket (especially when young being in small enclosed dark spaces calms them down).
He'll come around, don't worry
