The FX was the first of the "F" body Canon SLR cameras. These are the cameras that followed the original Canonflex. The basic FX "chassis" spawned the FP, Pellix, FT, TL and eventually the FTb TLb, TX and others. The FX was the first camera that took the Canon FL lens line. FD lenses will also fit on the FX and any other "F" bodied Canon SLRs'.
I'v got two Canon FX cameras. All metal, mostly hand-built, and very rugged with no design problems that I know of. An excellent camera that, like most of the cameras built in the 1960's, are built like a fine scientific instruments. Your 58/1.2 is a OK lens but no better. Terribly soft wide-open, it will sharpen up by F2.8 or so. The FL lens line was fairly complete and optically very good. Some of the lenses, like the FL-F series (using Fluorite elements) are outstanding even today.
Your camera may need a CLA, but other than that, will be a good solid picture taker. Enjoy.
Jim B.