There is one problem that I thought about yesterday with this "design". I wonder how he (if at all) managed the spot-killing. Since vector monitors are so intensely bright, there is a safety build into the deflection board (at least on the Amplifone) that if the beam would stop moving for any reason, it will immediately disable the beams. This is called the spot-killer.
If that disabling wouldn't happen, you would get a bad burned spot in the center of the screen very quickly.
I wonder if he thought about this. It should be possible to interface the signal to the RGB amps on the normal monitor PCB.
Alternatively, you could decide to never let this vector run without you watching it (but what if the doorbell rings, or you're getting a drink, plenty of time to kill the CRT)....