Good question, but I believe we have far more attacking options with Mortimer, Keating and Mateo sharing both sides of the ruck.
TBH, Mateo can play a 5/8ths role from lock anyway, so I reckon we are better served with all 3 on the field from the start.
Obviously, KK can play a rovers role throughout the game if needed.
Suity
Well when Hayne was playing fullback with KK in the halves he played alot more as a whole hitter rather than a first reciever and that would be his main role IMO.
In the line Hayne and Mateo will both probably play as a second 5-8 (Hunt like). KK and Mortz both seam to play better off 2nd phase play so I would like to see Mateo carrying the ball later in sets (3rd or 4th tackles rather than 1st or 2nd) and bring guys like KK and Mortz into play allowing them to feed guys like tahu, Inu and Reddy the ball earlier.