How important is it to match tubes in a preamp?

Sugarbrie, Bet the 12AU7 is a cathode follower? Just a guess, obviously.

In my experience the cathode follower contributes the least to sound quality. Try it and see, you can't do any harm - it may well work and save you money.

I'm not sure about your question, but designers aften design their circuits using the charastic's of specific tubes. As often as not the same pre-amp will have several different types of tubes serving several different purposes. Its not important so long as you keep the same type in each circuit as designed.