Don't limit yourself to the threads pertaining to the X-202-B. FISHER used a lot of common circuits in their lines, with minor modifications depending on the unit the circuit was installed in. Get the service manuals for the X-100-b, X-101-B, X-202, and finally the X-202-B and peruse the schematics. You'll notice a lot of common circuits in them, and as you go up the line more complexity in them.
I agree with NotDigital in that the X-202-B is a Gold Plated Bitch (my description but it fits) to work on and to get it right the 1st time. It's not really a unit that I would recommend for a 1st time restoration. Luckily, We have on the Forum one of the BEST (if not THE BEST)Tube Guru's that knows FISHERS inside and out, in Dave Gilliespie.
Please take some pictures of the unit, top and bottom, Outside and Insides (especially the insides). Quarter the bottom and take photo's of the sections. Make them close enough that we can identify items, and focused clearly. This will tell us a lot of things and we'll be able to tell you how far approximately you'll need to go to resurrect your grandfathers X-202-B.