K.M.
As I was reading your story, it sounded so much like my own. My step-son is 8. He's active, but inherited his father's and his grandmother's ADD. It wasn't so much of a problem until these past couple of years. It was hard in the beginning...me providing discipline, but my husband has really been supportive.
I would suggest (if you haven't already done so) that you and your significant other talk about disciplining...what's acceptable, what's not acceptable. Also, pick his brain for what he does when his son starts to get wound up. Once you and he are on the same page, then be consistent.
I've found that a simple time out works...sometimes after reminding my son to do something more than 3-4 times...I need a moment to regroup myself. This gives him time to think about what has happened and gives me time to cool down. When I'm on top of things, I ask him to help me do a couple things. I never give him more than 2-3 things to do at a time...on days when he's really wound up not more than 1 task at a time. Example, if we're at a grocery store, I'll ask him to go down the aisle and get one of the items on the grocery list. That way, he's moving around and being helpful. We have a routine. I have to provide the structure and remind him, but he has a checklist of chores so that he knows what's expected of him. Whenever I need him to busy himself for a while, I'll let him know the length of time and set a timer so that he can check for himself how much time is left, so that I can do whatever I need to do without interruption. Usually, it's for 30 min to an hour at the most.
Whenever there's good behavior or behavior that I'm looking for, then I praise it. (Hugs, high fives, or a simple great job or thank you) When my son gets overly excited, and starts bouncing around, I have him take 5 deep breaths while he puts his hands on his head. I do it with him. I calm down, he gets a kick out of it and calms down enough to tell me what he's so excited about. When my son is frustrated, I let him know that it's fine to be angry, but not to be destructive. My husband has a punching bag that gets used sometimes. Or we have him use his t-ball set up and hit some whiffle balls in the backyard. Once his angry energy is out, we talk about what has made him frustrated/angry/sad. Then I ask him what he can do about the situation and add some suggestions if he can't come up with anything or seems unable to see past the challenge to a solution. If he's gotten in trouble for something and is angry about being in trouble, then we sit and talk about how he could have done things differently so that he wouldn't have gotten into trouble, and why he got into trouble. After these talks, I always give him a hug and let him know that I love him.
I hope this is helpful.