A lot of times initiation can be an issue for stroke surviviors. This is not always behavioral, but a cognitive change occuring froma stroke. That means that a person will intend to do some, but initiating the task may be difficult and you may need to help. There are many stoke survisor support groups that may benfit your father. You can look online, or go to ASHA.org and they may have more info. Hope that helps.
In addition to your greater involvement, I think your dad needs to get into some kind of outside social environment. (I'm assuming the stroke forced him to retire early from work.) He's at the very youngest end of the Senior Center spectrum, but might find an activity or two to interest him there. You didn't tell us much about how well he functions. Could he attend a class at a community college? Or could he at least take an Adaptive PE class at a community college? Or can you find a swimming program for physically challenged swimmers in your community?
Depending on how willing he is to work at exercises, you might look into the Vasa Method home program at www.brainstrokes.com
What I've seen is that most stroke patients have no ambition of their own. They need to be continually motivated and that can be fustrating for the caregiver. The anger your fathers suffers may be predictable. He knows he's not the same yet, he dosen't know how to fix what's wrong with him.
Maybe start out by taking him for walks after dinner (get his doctor's approval first). The walk should be healthy for him and may allow for some private conversation to start between you both. Listen to what he says and you may gain some insight to his feelings or what is really bothering him. Being able to talk about it might help him. You might also look for those things he did with you when you were young. Playing catch is great for rebuilding hand - eye coordination. Perhaps start out with a basketball. Fishing? Playing cards? Look for those things that will challenge his brain but not to the point of frustration due to failure. It's not easy and it WILL take time however, stick with it. NEVER GIVE UP! Good luck and let us know how he's doing every now and then.