If you love that amp as you say you do:
I wouldn’t be too concerned with tubes, it’s only expensive every few years.
think hard about rearranging things to fit them, perhaps near/behind your speakers, short speaker cables (less $ to try others in the future).
speakers: double power: your chance of finding a great deal, new or used, are increased by more options available at a high and/or a bit lower efficiency, again, now and future.
live long.