see if the necktube glows when powered on--if not, then there is a dead spot on that chassis somewhere so the tube isn't getting power. you'll have to fix that before you can determine the condition of the tube.
check the flyback (large black thing) on the chassis for cracks or any discoloration that looks like it doesn't belong there (20 years of grime is ok)
its almost certain you'll need a capkit and thats very minor so ignore the caps at this point.
the biggest thing is to ask yourself, can i get this monitor running with my resources and expertise (and ken layton's

)