1. Can i run the 96 ITR Camshafts with gsr cam gears and gsr (new) timing belt?
You should be able to as the ITR and GSR timing belts are the same, don't think the GSR gears will fit the ITR shafts, but I could be wrong. . .

2. Will i need to switch into ITR ecu?
Hard to say, but I think yeah. . . because you have the ITR block and and ecu will be looking for certain specs that are in that block that the GSR ecu wont be looking for. . . I would think if you got it tuned, you may be able to get away with it, but may run better if you swapt to ITR ecu. . .