There are very few people with NOS (really new) GEC KT-88. Over on Audio Asylum , however, there have been some comparisons between the NOS (tubes in excellent condition testing new) and the current production Gold Lion KT-88s. The current production tubes reportedly sound as good as the old tubes, if not better. Try searching the Tube Asylum for a thread comparing them.
I don't recall any comparisons with KT-120s.