I just retubed my MkIIb with JJ's form EuroTubes. You need to call them and tell them what version and config of the MkII (A,B or C: 60watts, no reverb for me). They made alot of variations (60watt, 100/60 watt, Simul etc...)
I love my new tubes, I had the 6L6's graded from early break up, so...