CNT, Thank's for the information. After closer inspection of the metal tag on the disk, it is stamped "G109". Apparently those decals someone put on are from a Krause disk. At least now we know what we have.
We did try your trick to losen the nut. We even had 4 ft pipes on the wrench. We would heat the nut red and it would move only 1/4 turn each time and then get tight again. So we finally had to burn it off. Al