According this
this web page the occolating hook and race is new and different on the 185, and I think the 99K had a few alterations over the decades too. They aren't exactly the same. I like the blond wood bases with extention table on the later 99s and 185s though. If you already have a few straight stitchers already I doubt you are missing something. You have to do some test sewing to find out :- )