Unreal level of American reserve (9)

I believe the answer is:

storybook

'unreal' is the definition.

'level of american reserve' is the wordplay.
'level of american' becomes 'story' (US term for a level in a building).
'reserve' becomes 'book' (booking is a kind of reserving).
'story'+'book'='STORYBOOK'

(Other definitions for storybook that I've seen before include "Child's reader; perfect" , "Collection of children's tales" , "Fabulous" , "Ideal" .)

I've seen this clue in The Times.

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