Model GE4PV-XT Generator Interlock Kit fits GE panels having a 2-pole horizontal throw main breaker spaced at approx. 2 1/4" above the gen breaker. Part of this 2 1/4" spacing is a 1" blank under the 2-pole main breaker.
 
The gen breaker will occupy the two positions on the top of the RIGHT branch breaker column as shown.