Tube replacement for Dynaco ST 70

I just purchased a highly modified Dynaco St 70 and it came with EH EL 34 and I would lke to replace them since I feel they are a liitle thin and veiled on the upper midrange and lower treble regions where the voices are produced. Any suggestions on replaceing them with tubes that will open up and unveil the voices. I can uses 6L6 or KT 66.
Firstly, I would encourage you to contact Will Vincent himself.

But my understanding is that his amps are incredibly close and true to the original Dynaco ST70. That being the case, this should not be considered a heavily modified unit.

Most would consider the EL34 more open than the 6L6, as opposed to veiled. Though as you also mentioned thin sound, if you seek more richness and body, you might want to give some consideration to the 6L6.

I would ask what 7199 tubes you are using in your unit? With the right tubes, powering an agreeable speaker, the only cause left for not finding happiness in a Dynaco ST70 would be a difficult room.
Can anyone comment on the gold Lion KT77 as a replacement for the EH EL 34 tubes. Upscale audio is recommending it
I usually trust Upscale's recommendations. I've only heard their KT-66, but I've heard nothing but good things about the 77 as well.
Exocet 954
I have Will's mod also and just got the KT 66. Can u tell me what the basis setting should be on them
Will Vincent recommends 1.40mV DC meter for KT66 and EL34 tubes. Just read your post today. Sorry for the late respond.