Personally, I'd hit the CTC-20 first!
I have always wanted to play with one of those! 6GH8As from hell!!
You don't know for sure right now that the FBT is bad, it may be, then you are in a really bad spot, cause it seems to be ultra unobtanium,
I would just replace any fried parts, and see if it can get HV without smoking anything, if it can, you are in luck, if not, move on, you only risk a few resistors and perhaps a HOT.