[Amps] Matching 8874's

[Martin Sole]

I have just done a deal, I think, to secure two boxed unused Eimac 8874
tubes for my Alpha 78 which of course uses 3 of them. A few questions.

Can I run the amp with either 1 or 2 tubes, either temporarily or
indefinitely?

Can I use a third tube from a different source and be reasonably confident
that all will be well?

Should I just sell the two new Eimacs to somebody with a 2 tube amp and
invest in 3 from a single source?

Thanks,
Martin, HS0ZED