Retubing an ARC VT100 mkll


Thinking of tube rolling my VT100 mkll. Currently using EH for both the 6922 input and 6550 output tubes. Less than 800 hours on the entire set, so its not that I need an entire retube, just looking to improve the sound if possible. What would give the biggest improvement, changing out the input or output tubes to KT88/90? Bear in mind I would need a closely matched OCTECT of either so bizarre/rare vintage tubes are out of the question. Thinking of Gold Lions or similar, any thoughts from the scholars?
spinaker01
FYI:
I spoke also to ARC. No problems were anticipated. The new bulletin about compatibility from ARC was issued in the Feb/March 2012 period.
Awesome. Well they don't keep me in the loop. So the issue isn't whether the amp can handle the increased heater current because it can, the issue is the fact that the tubes are mounted horizontally. Because the KT-120 is longer and heavier, there is a risk of tube sockets loosening up to the point where the tube looses contact with the socket and the tube arcs. That is basically the issue. That is why ARC does not support the use of KT-120's in that amp. BTW it does sound very good with KT-120's.
Hmmmm.....so now I'm torn between the KT88 Gold Lions or, for similar money, the Tung-sol KT120. Hifigeek1, if you were going this route, which would you likely go with? Thanks!