May I ask what you are trying to do ? I don't mean that in a a-hole way, just more of a "I don't think I would want to mess with a REPR upper drastically.
I "think" it might fit... you might consider e-mailing MI and ask them
That said, I would "think" a MI receiver rod would work. From what I can tell...Your REPR upper appears to use a typical 308 CH track dimension-ally, appears to be typical 308 bolt lug setup, and a typical bolt to receiver extension interface.
Be aware... you might need to remove some material on the MI's top "fin", if it is a tight fit.