The problem I have is that even pages need to
have exactly 24 lines and odd pages exactly 20.
There is no problem with the diferentiation
between even and odd pages, but I don't know a
way to control the lines perpage.

Is there some?

Not explicitly by the way you are asking the
question ... there is no explicit control of "lines per page".

In fact, the document don't use tables. It have
a text like format, with blocks, paragraphs and
lines. Block titles count one line, and there aren't white lines at all.

Sounds like all you have to do is set the line
height accordingly, with a body region for even
pages sized to be 24 times the line height, and
the body region for odd pages sized to be 20
times the line height, then flowing the lines with your content.

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