If the neckboard is broken, are you sure the tube is okay? I'm gonna place a bet saying "NOPE".
Did you hear the sudden loss of vaccuum pressure accompanied by the cracking of the tube?
Look closely at the neck of the tube next to where the neckboard attachs. I'm willing to be the tube is toast.
Even if there isn't visible damage (I would find it so hard to believe if the drop was sufficient to break the neck board), there may be bent pins on the back, and that may cause the vaccum to be released.
I'm just pointing this out, because if you go through *all* the trouble of repairing the neck board [which I wont get into here] you may find yourself presented by a lightning show inside the tube once you reconnect it, before it dies and takes the rest of the monitor board with it.
A dropped tube scares me.. especially when it was enough to crack a PCB, which assuming it was connected to the tube means the tube sustained a large amount of force at its absolute weakest point.
I'd actually cut your losses and just go find a free or cheap 19" TV tube from the 80's (check thrift stores, houses on garbage day, rummage sales), and then go to 8liners.com and buy a brand new chassis for ~$73 shipped for a 19" one, mount the tube and chassis in your existing frame and be on your way again with probably a much clearer monitor with new electronics.
[Side note:] Why people want to spend big money refurbing old chassis (besides cap kits) is beyond me when you can get an old tv for virtually nothing and a chassis with brand new electronics for < $75, for between $75 and $100 you've got a new monitor with actually less work in the long run. (See the "whoooo mama" thread in this forum for more info on the 8liners chassis). I can understand in keeping a system "original" if it works, but spending hours resoldering and new flybacks and what not for the cost of a new one doesn't make too much sense in many cases.