Hi KTM and welcome to the forum. I have the parts manual for the #7 and it shows the same subframe for 755/855/955. Different models for each of 650, 750, 670 and 770. 850 is not listed but neither is my 790 (probably the same as the 770). So, not sure what to tell you. Maybe a Deere dealer has a better cross reference? Do you know what the lineage of the 850 was?
Wait, I just looked further into the catalog and it shows parts for the 850 with the #8 backhoe. Frame is common to 850, 950 and 1050. You sure you have a #7? Can you find a part number on the subframe?