compact tube amp and in wall speaker

"The speakers will be built into the bookshelf with their own wood enclosure matching the shelving. I would also consider a compact bookshelf speaker but my max height is 11 inches and max depth 13 inches icluding cabling."

You need to do some experimenting. Putting a bookshelf speaker in a bookshelf will have a huge impact on how it sounds. I know that sounds silly, but the vast majority of bookshelf speakers were never meant to be put in a bookshelf. Maybe get a cheap pair of Pioneer or Polk from Best Buy just to see what you're getting into. You can always return them, or trade up to the ML in walls you first mentioned.

@Zd542: yes, the more I get into this design, I realize compromises of what is a lifestyle type situation where I'm trying to get much better quality.I though maybe someone may have dealt with similar situations. Again appreciate the feedback as it helps sort the issues.

Audiouny, I would really opt against installing in-wall speakers in a bookshelf. They were not designed to be installed that way and will sound awful. Also, the money spent having a carpenter build them in will be better spent on better bookshelf speakers.
Go look at nice little bookshelf speakers that are either front ported or not ported. Rear ported will never work. For an amp, look at a tube hybrid like a peachtree.

If I get a efficient in wall or bookshelf, will 10 tube watts drive high 80's low -90 dB speakers?

You sort of answered this question already- high 80s is not efficient, nor for that matter is the low 90s (that might considered medium efficiency). If you want a 10-watt amp to do the job, higher efficiency is recommended (but of course a lot depends on how loud you intend to play).

Thank you for continued input. Here's where I'm at: considering Glow tube amp ( 1 or2), or Jolida fx 10 or 102rc, or 202brc if I can get one used in my price range. I have abandoned the in wall speaker idea and am considering glow speakers (cool bullet design), ZU cube (very efficient at 98db). I looked at and liked Omego super3''s (bottom ported; but too tall). I am setting up for a future compact subwoofer in a lower shelf or maybe triad in floor.

Has anyone experience with glow amps or speakers? I would need to balance the cost of the zu''s with hopefully a less expensive amp because of their high efficiency, although I need to check impedance at lower frequency of zu's. The glow amps come with an inexpensive dac and USB connection. Certainly learning a few things, hopefully making progress.