Jadis JA 50s power tubes


I contacted Jadis in France regarding the possibility of using KT-120 power tubes for my JA 50s. I received a response from Patrick Calmettes saying only KT-90s should be used in the amps due to high voltages. However, my amps have been using EH KT-88s, which they were supplied with upon purchasing them used from a very knowledgeable Jadis technician in NY. The amps are self-biasing....anyone have any experience using these amps?
lula
Nobody has any experience with JA 50 amps?
Even if it was ok to use, are you sure they fit? KT 120 tubes a little wider than KT 88 that you currently are using, right?
I'm accepting the info from Jadis that KT 120s can't be used....not sure if the physical size would be a problem. What I am questioning is the insistence on KT 90s, since I've been using KT88s. I want to try Gold Lion KT88s and see how they compare with the EHs.