You've got to realize that this isn't a high performance airplane and there is a limit to what the airframe will physically do. You could do any or all of the modifications you suggested and I doubt you would increase the roll rate much. You can only push a certain type of plane so far. I know it's probably not what you want to hear, but unfortunately it's the reality of your situation.

If you want that kind of performance it's time to change to a different type of plane

Ken