What about the low power input tubes? Also is this a Mk 1/2 or Mk3 model? If Mk3,there is no real ability to tube roll the 6H30's as there are (virtually)no options for replacement of these. If the earlier Mk1/2 variant, then they use the very common 6922 which can be changed but again, finding two truly matched quads of these is going to be difficult and VERY expensive. Would stick with common modern offerings like Gold Lion or similar. Good luck.