Well . . .. I read all about discharging the CRT, and have been working on iMacs for a few years now with no problems. I never take a CRT apart, but I remove and replace them all the time. The most important thing that I have found is that you need to ensure you don't have the computer plugged in, and then wait 30 minutes to an hour before you even discharge the CRT. There is information on how to do this on the web. As for replacing the FBT, I have NOT tried to do that. It is on the video board, and my experience is that you should just find an iMac that has a good PAV board and swap. In fact, the easiest thing to do is just buy another 333 and swap hard drives. In fact, why not move up to a slot-loader? If you find a 333 out there that is listed as needing repair, but with a working video board, that would be an option as well. Good luck, but as everyone has said, BE SAFE.
I, MacMan