#!/usr/bin/sed -f

# Range is from a blank line to <SB>.+
/^$/,/<SB>.+$/ {

   # Sub a blank line with <SB>\n
   s/^$/<SB>\
/

  # Find <Page.*, and swap with the line below
  /<Page.*/ {
    N
    s/\(<Page.*\)\n\($$$.*\)/\2\
\1/
  }

  # Kill the <SB> (I don't know why .* instead of .+ only works.)
  s/^<SB>\(.*\)$/\1/

}