Follow the header lines with an end-of-header line. An end-of-header line looks like this:
@c %**end of header
If you include the @setchapternewpage command between the
start-of-header and end-of-header lines, TeX will typeset a region as
that command specifies. Similarly, if you include an @smallbook
command between the start-of-header and end-of-header lines, TeX will
typeset a region in the "small" book format.
See section Start of Header.