Oh, I feel for you :(
Yes, you're right about the grief displacement. You are perceptive! However, I'm also sure you miss your Dad for real. He was everything 'Mike' should have been but wasn't. He protected and healed you - and your mother - from Mike's damage as far as possible. It's only natural that you long for his protection now, when everything's so raw. Please, do let yourself wallow in this for a while - thoughts of your Dad might help you relive some of those feelings of love & safety.
Flashbacks are nasty ... and they are 'invitations' from your mind to deal with some of the fear, anger and hurt you suffered (and still do) with Mike. Please see if Pete Walker's flashback guide offers any support - it's pinned on my kitchen wall, but everybody's different and it may not be right for you just now; have a look.
As to grieving for Mike - or, perhaps more accurately, for your childhood self and the father you should have had then - it's a flaming nuisance that he won't go away for real! You might want to begin dealing with this by writing down some of the ways he betrayed you and your thoughts about that. I'm wary of suggesting this before you've got the support of a counsellor, however you could get out a pen and paper to see if anything wants to write or draw 'itself'. You can always throw the paper away afterwards. Make sure you are safe, comfy and have friendly contact to hand if you try it, just in case it proves too upsetting.
I think you'll want, at some point, to conduct an emotional 'funeral' for Mike although that will probably come when you have counselling and more tools in your psychological workshop! I was fortunate, in a peculiar way, that I had the opportunity to do this at my father's real funeral. I do believe you'll be able to do it, given the right amount of time, without waiting around for the real event.
While typing this, I have the feeling I've crossed some sort of line and have put things badly. I hope not, and that you'll forgive me for any insensitivity. Next respondent, please correct me where necessary!!
Thank you for your update, roadkill, and do remember to treat yourself with great kindness.