Sounds to me like you are spending too much time in your head making comparisons. He's not your father and never will be. I doubt he's even trying to fill those shoes for you. It sounds like he's just trying to be a partner to your mother and you. Let him. Allow him his mistakes. It's likely his financial burden too and he recognizes that, which is why he wants to do as much as he can himself.
Help him. If you spent time working with your father, you prob'ly have loads of good experience you can share with your step-father. Don't be stingy with it. I bet he would really enjoy working with you, especially if he knows you have some experience to offer the projects. Don't make the mistake of letting him blunder through without your expertise, maybe hoping it will make him look bad. It won't. Your mother prob'ly knows you could lend a hand to avoid the worst mistakes, so it'll be you that looks bad.
Yeah, like inspectorD said, it's a bonding project - you and the new step-father. Give it time and try to be patient and tolerant. Your mom is.
Best R'gards,
Jim