Since you have the benefit of the horizontal hanger I'll bet you can get away with it. The trick to go over-capacity with the Campy NR is to slide the axle back in the dropout so the upper idler pulley doesn't tangle with the freewheel sprocket. Running 52/42 up front and a 13-26 in back means you need to wrap 23 teeth of chain, and the listed capacity is 24 teeth, so you should be okay.