I really have no ideal about 6v6 tubes. I know only 6V6 JJ's are approved so compare the the specs. Worst that can happen is you blow a fuse or a tube.
I would stick with JJs. I used some Groove Tubes and I think they were Sovteks... its hard to keep up with GTs... and I toasted them in my old RM100. I have used JJs and they work great. I biased them at 19.