More suggestions. For a faster, tighter sound, Telefunken tubes would also work well for the 12AX7 positions (marked ECC83 or as 12AX7). For the 12AT7 position, perhaps a 5751 would be a good choice. The 5751s could also be used in the 12AX7 positions, but, they offer lower gain than a 12AX7. The Hovland appears to have plenty gain so that is not a big deal.
Unfortunately, these older tube types are not cheap, particularly when compared to current production tubes. But, in my opinion, the Hovland is worthy of the better vintage tubes out there.
Good luck on your search.