Hi John .....
I have rolled out all the original tubes, and I think I have successfully modified the amp to give me a better overall sound of music (of course, to my ears and in my room.) With the thoughtful guidance and advice of Mark O'Brien and Nick at Rogue Audio, I swapped out the five small tubes as follows : an RCA NOS 5814 to replace the Electro-Harmonix 12AU7 gain stage tube, a pair of GE NOS Five Star 5751 "goldpins" to replace the Sovtek 12AX7 input tubes, and a pair of GE NOS 12AU7A's to replace the Electro-Harmonix 12AU7 driver tubes. I then replaced the original Svetlana EL-34's with a wonderfully matched quad of Genelex Gold Lion KT-77's.
And ..... I really love the sound of music now, with nothing that I want to change. So, staying with the GL's probably makes the most sense