Dan,
Yes, the inability to focus is most likely due to the 'floating' deflection plates. Connect all four, pins 7, 8, 10 & 11 via 1M resistors each to pin 9. The value isn't important, anything from 100k to 1M will be fine.
Here's a link that might be useful..
http://members.chello.nl/~h.dijkstra19/page3.html
Also this for general data on CRTs of all types...
http://en.wikipedia.org/wiki/Cathode_ray_tube
Steve A.