The text on p. 4 ends with rhyming T words: trail and tail. If "Tea for Two" and "Two Together" are telling us to focus on double-Ts, this could be relevant.
The text says, "now that you and I have crossed / Paths." Draw a path from U to I? (Sort of an "an eye reflects" approach?) There is a U directly opposite the letter I in the border phrases along the sides: cU
nning to hI
s. These are common letters, but you can make similar U/I pairs on other pages as well, often with a line parallel to the border (although not always) and often the only U/I pair on the page:
p. 7 - sceptre I
n hand to i rU
le the sea
p. 11 - a measU
re of gold to a gI
ft for the wInd (this one could make two U/I pairs, since there are two letters I on the right border. If a U/I pair is part of the point, maybe this would explain why the QU and IN are combined in the magic square - the authors are telling us that the magic square does not contain a relevant U/I pair.)
p. 15 - crI
ss cross to doU
p. 17 - one of foU
r to all I
n a name
p. 19 - an eye
reflects to coU
nt to three (this one works only if eye = I. Or it could be a red herring page.)
p. 23 - raI
se the wI
nd to whistle a tU
p. 26 - we cast oU
r spell to follow the lI
p. 30 - no letter U in the border. Could be a U/I pair using words on books or map? I see "Down U
re Island," "Robert LoU
is Stevenson," "Pemetic Mou
ntain," "St. Sau
ntain," and two letters U on the wine bottle - LU
ssac and BoU
teille. The word "mountain" is abbreviated in all the other places on the map and the word "Norumbega" is artfully cut off the show only "-bega." Still a number of possibilities, but I wonder whether there is something deliberate here. If the border word "map" is telling us that only the letters U on the map are important, that further reduces the possibilities.
p. 32 - The Abnaki illustration is the first place where I see both an I/U and a U/I possibility, with both letters on opposite borders:
re to rI
n a qU
If "you and I have CROSSED
paths" is important, this is the first clear case of a possible cross, unless I'm mistaken.
p. 34-35 - no letter U in the border.
p. 40 - no letter U in the border.
p. 44-45 - The only letter U in the border is in "toUr with me." There is no I in the opposite border. Use mile marker letters?
p. 47 - topsy tU
rvy to upsI
p. 51 - the second possible crossed path: a tU
rning tide to a taI
l to tell; a fallI
ng sky to at joU
Note on the text: 'What else have you
p. 55 - No letter I in the border.
I don't yet see a clear pattern of things crossed by these U/I lines, although several go through or near eyes.
My other unexplored thought is whether "Whistle a Tune" and "Neptune" are related. I'm sure others have pondered this already. If the root word is "Tune," maybe we are supposed to sort out the meaning of "Nep-" - if it could also be "pen," maybe that pencil eraser in the sand on p. 7 is telling us to pair it with a sill? Which would suggest the Old Lady's window sill to me. But I really feel now like I'm building a theory on random, meaningless word associations and coincidences.