Personally, I agree with the posters at the electro-tech forum:
...IOW, don't waste your time, unless you have a need to learn how to build an analog scope for some reason. Not only will your horizontal timebase be limited, but you'll also run into a host of other issues, plus there's always the chance of electrocution. I would also forget about the idea of converting to electrostatic deflection; that generally needs the plates -inside- the glass envelope of the CRT...
You will likely spend a lot of time and effort to end up with a mediocre system at best; if learning how to build an analog scope is what you are going for, then maybe it might be worth it. Otherwise, save you time and money; there are plenty of used low-cost 2 channel analog scopes out there to be had for fairly cheap.
Otherwise, you might be better off purchasing a DSO nano, or some other kind of DSO kit scope - or build one with the Arduino and a KS0108 graphic LCD.