identify possible 3rd arginine/glutamine sidechain -- very weak and overlapped:

 - merge spin systems
 - pick new NHSQC peaks
 - retag peaks
severely overlapped peaks in NHSQC but apparently a real peak in HNCO:  pick a matching peak in NHSQC and add both to a new spin system
add new HNCO peak based on strong NHSQC signal that had no matching HNCO peak, and add to spin system; remove an artifact HNCO peak from its spin system