Custom Display for system.object Editor

I have a data type called Action in my game, which has three attributes:

 public class Action
 {
     public string methodName = "";
     public object parameter = null;
     public int frame;
 }

I want to be able to edit the values of these from the inspector to help speed up my development process. I can freely edit methodName and frame. However, because the parameter field is an object, it can't be displayed in the inspector. All I would like the inspector to do for Action is to go down a list of types ( int, string, another Action, etc.) and display it based on if it matches anything, otherwise, not display at all. (If it's an int, use Unity's default behavior for drawing an int.)

I've done some digging around and things like CustomEditor and PropertyDrawer look promising, but I haven't been able to get anything figured out yet. Has anyone been able to work through this? Thanks in advance.