As far as I recall (being at home now), the NPCONFIG.PUB.SYS
does provide an entry where you can define the tcp_port_number
in addition to the network_address (the default port number
used is some reasonable ninethousand-something value).
Check NPSAMP1.PUB.SYS or NPSAMP2.PUB.SYS -- they might contain
a useful example. Otherwise the Native Mode Spooler manual
should do (as it has new chapters on JetDirect spooled printers)
Regards, Lars.