Modifications
The biggest modification for my unit is simply the books that I choose for this reading level group. After watching this group of students read, I had a fairly good idea about their instructional reading level. From this I found three books that would be challenging in some ways for them, but also easy enough so that they aren't in their frustration level reading them.
Since the group that I am working with is the lower level reading group, I also plan to explain the jobs to them several times during the course of the unit. While the higher level reading group only needs the jobs explained once or twice, these students need to be reminded of what is expected of them so that they have a clear idea of what you are looking for in their work.
As they do the jobs throughout the unit I will also be continually checking with them to make sure that they are doing what they need to be doing. These students need the instruction and to be checked on while they are doing their jobs until they feel confident with the material and know what is expected of them.
Some of your students may need to hear the story out loud to be able to comprehend it. In this case I would record myself reading the book and let them follow along while hearing my voice. This way I am able to model to them proper reading techniques.
Another strategy is simply to modify your job roles. For some students five questions for the Discussion Director is simply too difficult for them to accomplish. Have them only make up 2 or 3 in these circumstances.