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.
JJ E34L as suggested above are a well extended and well well balanaced EL34 type that works well in the Dynaco. They can be had for a very good price from I like the blue glass versions . I have been using them for years.
I own one of Will Vincent "Audiospec" Stereo 70's.
Recently upgraded the output tubes to the Gold Lion KT66
and have not looked at other EL34 tubes. The soundstage just opened up. With this amp the improvement is huge.
All the best....
I realized I only listed EL34's. If your amp will accommodate them with the mods, the Gold Lion KT-66 reissues are outstanding - probably the best bang for the buck and one of the best 2 or 3 options available.
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.